There is an urgent global need for electrochemical energy storage that includes materials that can provide simultaneous high power and high energy density One strategy to achieve this goal is with pseudocapacitive materials that take advantage of reversible surface or near-surface Faradaic reactions to store charge This allows them to surpass the capacity limitations of electrical double-layer capacitors and the mass transfer limitations of batteries The past decade has seen tremendous growth in the understanding of pseudocapacitance as well as materials that exhibit this phenomenon The purpose of this Review is to examine the fundamental development of the concept of pseudocapacitance and how it came to prominence in electrochemical energy storage as well as to describe new classes of materials whose electrochemical energy storage behavior can be described as pseudocapacitive

Pseudocapacitance: From Fundamental Understanding to High Power Energy Storage Materials

https://www.cell.com/chem/pdf/S2451-9294(19)30219-0.pdf

Polymer Electrolytes for Lithium-Based Batteries: Advances and Prospects

Electrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.202001239

Heteroatom-Doped and Oxygen-Functionalized Nanocarbons for High-Performance Supercapacitors

Lithium (Li) metal is one of the most promising alternative anode materials of next-generation high-energy-density batteries demanded for advanced energy storage in the coming fourth industrial revolution. Nevertheless, disordered Li deposition easily causes short lifespan and safety concerns and thus severely hinders the practical applications of Li metal batteries. Tremendous efforts are devoted to understanding the mechanism for Li deposition, while the final deposition morphology tightly relies on the Li nucleation and early growth. Here, the recent progress in insightful and influential models proposed to understand the process of Li deposition from nucleation to early growth, including the heterogeneous model, surface diffusion model, crystallography model, space charge model, and Li-SEI model, are highlighted. Inspired by the abovementioned understanding on Li nucleation and early growth, diverse anode-design strategies, which contribute to better batteries with superior electrochemical performance and dendrite-free deposition behavior, are also summarized. This work broadens the horizon for practical Li metal batteries and also sheds light on more understanding of other important metal-based batteries involving the metal deposition process.

Review on Li Deposition in Working Batteries: From Nucleation to Early Growth.

The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors.

Electrode Materials for Supercapacitors: A Review of Recent Advances

Capacitive mechanism of oxygen functional groups on carbon surface in supercapacitors

Ion association tailoring SEI composition for Li metal anode protection

A novel ZnO-based inorganic/organic bilayer with low resistance for Li metal protection

Mo particles have been introduced into Ag–Cu–Ti brazing alloy for the joining of Si3N4 ceramic. Effect of brazing temperature on microstructure and mechanical properties of the joints were investigated. The result shows that a continuous reaction layer which is composed of TiN and Ti5Si3 was formed at the Si3N4/braze interface. The central part of the joint was composed of Ag-based solid solution, Cu-based solid solution, Mo particles, and Cu–Ti intermetallic compounds. By increasing the brazing temperature, both the thickness of the reaction layer and amount of Cu–Ti intermetallic compounds in the joint increased, being beneficial for the joint strength. Whereas, the reaction between Ti and Si3N4 ceramic proceeded excessively and more Cu–Ti intermetallic compounds were precipitated in the joint while elevating the brazing temperature to 950 °C, leading to deterioration of the bending strength. The maximal bending strength reached 429.4 MPa at 900 °C for 5 min when the Si3N4 ceramic was brazed with Ag–Cu–Ti + Mo composite filler.

Effect of brazing temperature on microstructure and mechanical properties of Si3N4/Si3N4 joints brazed with Ag–Cu–Ti + Mo composite filler

The present study investigated the effect of brazing temperature and holding time on the microstructure and mechanical properties of Ti 2 AlC-copper joints brazed with Ag-Cu filler alloy at 800–900 °C for 10 min and held for different times at 850 °C. The representative structure of the joints was Ti 2 AlC/interaction area in the Ti 2 AlC substrate/brazing layer/diffusion area of the copper substrates/Cu. The brazing layer was composed of Cu-rich phases, AlCu 2 Ti intermetallic compounds and Ag[Cu] solid solutions. With increasing brazing temperature, more filler alloy was infiltrated into the ceramic substrate and reacted with Ti 2 AlC, accelerating the decomposition of Ti 2 AlC and the formation of Ti 3 AlC 2 , TiC and AlCu 2 Ti reaction phases. Moreover, more copper substrate was dissolved into the filler alloy; thus, more Cu-rich phase and AlCu 2 Ti were produced in the brazing layer. Moreover, the width of the brazing layer was reduced, while the widths of both the interaction area and diffusion area increased. As the brazing temperature was increased, the shear joint strength increased and then decreased. By prolonging the holding time, the widths of both the interaction area and the diffusion area were increased, while the width of the brazing layer was held constant at approximately 50 μm. Neither the structure nor the shear strength of the joints was influenced by the holding time. The optimum brazing parameters for joining Ti 2 AlC ceramic to copper with Ag-Cu filler alloy were 850 °C for 40 min. The joints obtained exhibit a maximum shear strength of 203.3 MPa.

Yitao He

Papers

Capacitive mechanism of oxygen functional groups on carbon surface in supercapacitors

Ion association tailoring SEI composition for Li metal anode protection

A novel ZnO-based inorganic/organic bilayer with low resistance for Li metal protection

Effect of brazing temperature on microstructure and mechanical properties of Si3N4/Si3N4 joints brazed with Ag–Cu–Ti + Mo composite filler

Effect of joining temperature and holding time on microstructure and shear strength of Ti2AlC/Cu joints brazed using Ag-Cu filler alloy