Direct Ink Writing 3D Printing for High-Performance Electrochemical Energy Storage Devices: A Minireview.

Despite tremendous efforts that have been dedicated to high-performance electrochemical energy storage devices (EESDs), traditional electrode fabrication processes still face the daunting challenge of limited energy/power density or compromised mechanical compliance. 3D thick electrodes can maximize the utilization of z-axis space to enhance the energy density of EESDs but still suffer from limitations in terms of poor mechanical stability and sluggish electron/ion transport. Direct ink writing (DIW), an eminent branch of 3D printing technology, has gained popularity in the manufacture of 3D electrodes with intricately designed architectures and rationally regulated porosity, promoting a triple boost in areal mass loading, ion diffusion kinetics, and mechanical flexibility. This focus review highlights the fundamentals of printable inks and typical configurations of 3D-printed devices. In particular, preparation strategies for high-performance and multifunctional 3D-printed EESDs are systemically discussed and classified according to performance evaluation metrics such as high areal energy density, high power density, high volumetric energy density, and mechanical flexibility. Challenges and prospects for the fabrication of high-performance 3D-printed EESDs are outlined, aiming to provide valuable insights into this thriving field.

Adjusting the 3d Orbital Occupation of Ti in Ti3 C2 MXene via Nitrogen Doping to Boost Oxygen Electrode Reactions in Li-O2 Battery.

Rationally designing efficient catalysts is the key to promote the kinetics of oxygen electrode reactions in lithium-oxygen (Li-O2 ) battery. Herein, nitrogen-doped Ti3 C2 MXene prepared via hydrothermal method (N-Ti3 C2 (H)) is studied as the efficient Li-O2 battery catalyst. The nitrogen doping increases the disorder degree of N-Ti3 C2 (H) and provides abundant active sites, which is conducive to the uniform formation and decomposition of discharge product Li2 O2 . Besides, density functional theory calculations confirm that the introduction of nitrogen can effectively modulate the 3d orbital occupation of Ti in N-Ti3 C2 (H), promote the electron exchange between Ti 3d orbital and O 2p orbital, and accelerate oxygen electrode reactions. Specifically, the N-Ti3 C2 (H) based Li-O2 battery delivers large discharge capacity (11 679.8 mAh g-1 ) and extended stability (372 cycles). This work provides a valuable strategy for regulating 3d orbital occupancy of transition metal in MXene to improve the catalytic activity of oxygen electrode reactions in Li-O2 battery.

Synergy of cobalt vacancies and iron doping in cobalt selenide to promote oxygen electrode reactions in lithium-oxygen batteries.

Electronic structural engineering plays a key role in the design of high-efficiency catalysts. Here, to achieve optimal electronic states, introduction of exotic Fe dopant and Co vacancy into CoSe2 nanosheet (denoted as Fe-CoSe2-VCo) is presented. The obtained Fe-CoSe2-VCo demonstrates excellent catalytic activity as compared to CoSe2. Experimental results and density functional theory (DFT) calculations confirm that Fe dopant and Co defects cause significant electron delocalization, which reduces the adsorption energy of LiO2 intermediate on the catalyst surface, thereby obviously improving the electrocatalytic activity of Fe-CoSe2-VCo towards oxygen redox reactions. Moreover, the synergistic effect between Co vacancy and Fe dopant is able to optimize the microscopic electronic structure of Co ion, further reducing the energy barrier of oxygen electrode reactions on Fe-CoSe2-VCo. And the lithium-oxygen batteries (LOBs) based on Fe-CoSe2-VCo electrodes demonstrate a high Coulombic efficiency (CE) of about 72.66%, a large discharge capacity of about 13723 mA h g-1, and an excellent cycling life of about 1338 h. In general, the electronic structure modulation strategy with the reasonable introduction of vacancy and dopant is expected to inspire the design of highly efficient catalysts for various electrochemical systems.

A multifunctional protective layer with biomimetic ionic channel suppressing dendrite and side reactions on zinc metal anodes.

A multifunctional graphitic carbon nitride (GCN) protective layer with bionic ion channels and high stability is prepared to inhibit dendrite growth and side reactions on zinc (Zn) metal anodes. The high electronegativity of the nitrogen-containing organic groups (NOGs) in the GCN layer can effectively promote the dissociation of solvated Zn2+ and its rapid transportation in bionic ion channels via a hopping mechanism. In addition, this GCN layer exhibits excellent mechanical strength to suppress the growth of Zn dendrites and the volume expansion of Zn metal anodes during the plating process. Consequently, the electrodeposited Zn presents a uniform and densely packed morphology with negligible side-product accumulation. As a result, the half-cell composed of the Cu-GCN anode can deliver a remarkable long-term cycling performance of 1000 h at 0.5 mA cm-2 and 0.25 mAh cm-2. A full cell assembled with MnO2 cathode also displays improved long-term cycling performance (150 cycles at 200 mA g-1) when the Cu-GCN@Zn composite anode is applied. This work deepens our understanding of the kinetics of ion migration in the interface layer and paves the way for next-generation high energy-density Zn-metal batteries (ZMBs).

Adjusting the d-band center of metallic sites in NiFe-based Bimetal-organic frameworks via tensile strain to achieve High-performance oxygen electrode catalysts for Lithium-oxygen batteries.

Developing effective electrocatalyst and fundamentally understanding the corresponding working mechanism are both urgently desired to overcome the current challenges facing lithium-oxygen batteries (LOBs). Herein, a series of NiFe-based bimetal-organic frameworks (NiFe-MOFs) with certain internal tensile strain are fabricated via a simple organic linker scission strategy, and served as cathode catalysts for LOBs. The introduced tensile strain broadens the inherent interatomic distances, leading to an upshifted d-band center of metallic sites and thus the enhancement of the adsorption strength of catalysts surface towards intermediates, which is contributed to rationally regulate the crystallinity of discharge product Li2O2. As a result, the uniformly distributed amorphous film-like Li2O2 tightly deposits on the surface of strain-regulated MOF, resulting in excellent electrochemical performance of LOBs, including a large discharge capacity of 12317.4 mAh g-1 at 100 mA g-1 and extended long-term cyclability of 357 cycles. This work presents a novel insight in adjusting the adsorption strength of cathode catalysts towards intermediates via introducing tensile strain in catalysts, which is a pragmatic strategy for improving the performance of LOBs.

Boosted Li+ transference number enabled via interfacial engineering for dendrite-free lithium metal anodes.

Adverse dendritic growth destabilizes Li metal anodes (LMAs), dramatically limiting the commercial applications of Li metal batteries (LMBs). Herein, ZIF-67 with unsaturated coordinative metal sites is used to construct a protective coating to immobilize anions, which is capable of increasing the Li+ transference number (tLi+) to mitigate the electrolyte concentration gradient in the vicinity of LMAs. In addition, the ZIF-67-based layer provides highly ordered ionic diffusion pathways, thus enabling dendrite-free Li deposition. With a considerable Li+ transference number of 0.57, ZIF-67-Cu@Li symmetric cells deliver a superior long-term performance (over 1000 h), and Li-O2 full batteries with ZIF-67-Cu@Li electrodes display a high energy density of 1911.61 W h kg-1.

Adjusting the Covalency of Metal-Oxygen Bonds in LaCoO3 by Sr and Fe Cation Codoping to Achieve Highly Efficient Electrocatalysts for Aprotic Lithium-Oxygen Batteries.

Developing high-efficiency dual-functional catalysts to promote oxygen electrode reactions is critical for achieving high-performance aprotic lithium-oxygen (Li-O2) batteries. Herein, Sr and Fe cation-codoped LaCoO3 perovskite (La0.8Sr0.2Co0.8Fe0.2O3-σ, LSCFO) porous nanoparticles are fabricated as promising electrocatalysts for Li-O2 cells. The results demonstrate that the LSCFO-based Li-O2 batteries exhibit an extremely low overpotential of 0.32 V, ultrahigh specific capacity of 26 833 mA h g-1, and superior long-term cycling stability (200 cycles at 300 mA g-1). These prominent performances can be partially attributed to the existence of abundant coordination unsaturated sites caused by oxygen vacancies in LSCFO. Most importantly, density functional theory (DFT) calculations reveal that codoping of Sr and Fe cations in LaCoO3 results in the increased covalency of Co 3d-O 2p bonds and the transition of Co3+ from an ordinary low-spin state to an intermediate-spin state, eventually resulting in the transformation from nonconductor LCO to metallic LSCFO. In addition, based on the theoretical calculations, it is found that the inherent adsorption capability of LSCFO toward the LiO2 intermediate is reduced due to the increased covalency of Co 3d-O 2p bonds, leading to the formation of large granule-like Li2O2, which can be effectively decomposed on the LSCFO surface during the charging process. Notably, this work demonstrates a unique insight into the design of advanced perovskite oxide catalysts via adjusting the covalency of transition-metal-oxygen bonds for high-performance metal-air batteries.

Surface atomic modulation of CoP bifunctional catalyst for high performance Li-O2 battery enabled by high-index (211) facets.

The rational design of the surface structure and morphology characteristics of the catalyst at atomic level are the key to improve the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in lithium-oxygen (Li-O2) battery. Here a series of cobalt phosphide (CoP) electrocatalysts with a variety of index facets are successfully prepared including concave polyhedrons CoP exposing with (211) crystal planes (CoP CPHs) spherical nanoparticles CoP exposed with (011) crystal planes and polyhedron particles CoP exposing with (011) and (111) crystal planes. The results show that CoP CPHs based Li-O2 battery presents a large discharge capacity of 33743 mA h g-1 at current density of 50 mA g-1 and a remarkable long cycle life of up to 950 h. The experimental results demonstrates that the CoP CPHs electrode exposing with high-index (211) facets based Li-O2 battery exhibits an extremely low overpotential (0.67 V) ultrahigh specific capacity (33743 mAh g-1) and remarkable long-term stability of up to 950 h. Most importantly density functional theory (DFT) calculations demonstrate the excellent electrocatalytic activity of high-index (211) facets as compared to the low-index (011) and (111) planes are because of the existence of large density of atomic steps edge ledge sites and kinks which supply a wide space for breaking chemical bonds and increasing the reaction activity for oxygen electrode.