Alternative Anode Material Research Articles

Seamlessly Merging the Capacity of P into Sb at Same Voltage with Maintained Superior Cycle Stability and Low‐temperature Performance for Li‐ion Batteries

Among the alloying‐type anodes, elemental Sb possesses the suitable yet safe plateau, simple lithiation pathway, small voltage polarization, high conductivity, and superior cycle stability. However, challenge is that its intrinsic capacity is rather low (660 mAh g−1), <1/6 of silicon. Herein, we propose a seamless integration strategy by merging the voltage and capacity of phosphorus and antimony into a solid solution alloy. Interestingly, the enlistment of P is found greatly enlarge the capacity from 660 to 993 mAh g−1 for such Sb30P30 solid solution, while maintaining a single and stable discharge plateau (~0.79 V) similar to elemental Sb. Various experimental characterizations including XPS, PDF, Raman, and EDS mapping reveal that in such a material the P and Sb atoms have interacted with each other to form a homogenous solid solution alloy, rather than a simple mixing of the two substances. Thus, the Sb30P30 exhibits superior rate performances (807 mAh g−1 at 5000 mA g−1) and cyclability (821 mAh g−1 remained after 300 cycles). Furthermore, such Sb60‐xPx alloys can even deliver 621 mAh g−1 at −30°C, which can be served as the alternative anode materials for high‐energy and low‐temperature batteries. This unique seamless integration strategy based on solid solution chemistry can be easily leveraged to manipulate the capacity of other electrode materials at similar voltage.

Search for New Anode Materials for High Performance Li-Ion Batteries.

Owing to an unmatched combination of power and energy density along with cyclic stability, the Li-ion battery has qualified itself to be the highest performing rechargeable battery. Taking both transportable and stationary energy storage requirements into consideration, Li-ion batteries indeed stand tall in comparison to any other existing rechargeable battery technologies. However, graphite, which is still one of the best performing Li-ion anodes, has specific drawbacks in fulfilling the ever-increasing energy and power density requirements of the modern world. Therefore, further research on alternative anode materials is absolutely essential. Equally important is the search for and enhanced use of right earth abundant materials for battery electrodes so as to bring down the costs of the battery systems. In this spotlight article, we discuss the current research progress in the area of alternative anode materials for Li-ion battery, putting our own research work over the past several years into perspective. Starting from conversion anode systems like oxides and sulfides, to insertion cum alloying systems like transition metal carbides, to molecularly engineered open framework systems like metal organic frameworks (MOFs), covalent organic frameworks (COFs), and organic-inorganic hybrid perovskites (OIHPs), this spotlight provides a complete essence of the recent developments in the area of alternative anodes. The possible and potential impact of these new anode materials is detailed and discussed here.

Effect of Cr doping on Li2ZnTi3O8 as alternative anode material to enhance electrochemical properties of lithium-ion batteries

Effect of Cr doping on Li2ZnTi3O8 as alternative anode material to enhance electrochemical properties of lithium-ion batteries

Designing of carbon cloth @ Co-MOF @ SiO2 as superior flexible anode for lithium-ion battery

Silica combining high theoretical specific capacity (1965 mAh g−1), abundant storage, light weight, small size, and no harmful substances has been recognized as an alternative anode material for lithium-ion batteries. However, low diffusivity of lithium ions, poor natural electrical conductivity and disappointing structural stability of silica represents a key problem that severely limits their practical applications. Herein, we report on designing a composite structure of CC @ Co-MOF @ SiO2, in which 3D porous and carbonized structure of cobalt-metal organic framework (Co-MOF) can adapt to the huge volume change of SiO2, inhibit the aggregation of SiO2 nanospheres and buffer mechanical stress. Meanwhile, SiO2 nanospheres with a smaller diameter not only restrain their own volume expansion but also enable more SiO2 nanospheres to occupy or attach to the void of the Co-MOF, resulting in an increase of the amount of active material in the electrode which can greatly boost the specific capacity of batteries. Carbon cloth (CC) as the substrate can effectively improve conductivity of CC @ Co-MOF @ SiO2 as well as stability of the structure and interface can be maintained to a certain extent. Profiting from the synergistic effect of the components, the CC @ Co-MOF @ SiO2 composite presents outstanding electrochemistry properties as electrode materials for lithium-ion batteries. The first discharge capacity of CC @ Co-MOF @ SiO2 is 1799.4 mAh g−1 at the current density of 1 A g−1. CC @ Co-MOF @ SiO2 composite material exhibits an outstanding reversible capacity of 1565 mAh g−1 at the current density of 1 A g−1 after 300 cycles and the capacity retention rate is even as high as 86.97%. The synergistic effect of the components of the CC @ Co-MOF @ SiO2 composite is also discussed. The present synthesis method can be easily extended to produce other CC @ Co-MOF based oxide composite for lithium-ion batteries or other applications.

Study of the dynamics of heating anode units in a maskless nanolithograph based on an array of microfocus X-ray tubes

In this paper, we study the dynamics of heating the matrix of anode nodes membrane with a transmission-type target under the action of a field emission current generated in the electronic system of a maskless X-ray nanolithograph. The promising membrane materials that provide the most efficient heat removal from the matrix have been determined, among which diamond-like films have shown the best thermal stability. At the calculated power of soft X-ray radiation P_X=2.5 nW, scattered by a pixel with a size of 20 nm and an X-ray resist irradiation dose D=100 J/m2, the exposure time was 25 μs. It is shown that during the exposure of a 150 mm plate, a diamond-like anode membrane with a size of 300x300 elements heats up from 20 to 62oC, which is 15-25 times lower than the heating temperature of alternative anode materials (Cu, Fe, Ni, Si, Al). The technological route for the fabrication of the matrix of anode nodes is described, taking into account the proposed methods for optimizing its design, aimed at reducing the thermal effects of heating during X-ray nanolithography processes. The results obtained can be applied in the development of a thermostable system of microfocus X-ray tubes as part of a maskless X-ray nanolithograph. Keywords: X-ray nanolithography, microfocus X-ray tube, transmission-type target, matrix of anode nodes, electron bombardment heating, thermal expansion, Bosch-process.

Low‐strain TiP2O7 with three‐dimensional ion channels as long‐life and high‐rate anode material for Mg‐ion batteries

AbstractRechargeable magnesium batteries are identified as a promising next‐generation energy storage system, but their development is hindered by the anode−electrolyte−cathode incompatibilities and passivation of magnesium metal anode. To avoid or alleviate these problems, the exploitation of alternative anode materials is a promising choice. Herein, we present titanium pyrophosphate (TiP2O7) as anode materials for magnesium‐ion batteries (MIBs) and investigate the effect of the crystal phase on its magnesium storage performance. Compared with the metastable layered TiP2O7, the thermodynamically stable cubic TiP2O7 displays a better rate capability of 72 mAh g−1 at 5000 mA g−1. Moreover, cubic TiP2O7 exhibits excellent cycling stability with the capacity of 60 mAh g−1 after 5000 cycles at 1000 mA g−1, which are better than previously reported Ti‐based anode materials for MIBs. In situ X‐ray diffraction technology confirms the single‐phase magnesium‐ion intercalation/deintercalation reaction mechanism of cubic TiP2O7 with a low volume change of 3.2%. In addition, the density functional theory calculation results demonstrate that three‐dimensional magnesium‐ion diffusion can be allowed in cubic TiP2O7 with a low migration energy barrier of 0.62 eV. Our work demonstrates the promise of TiP2O7 as high‐rate and long‐life anode materials for MIBs and may pave the way for further development of MIBs.

A non-redoxable electron-cloud-channel oxide electrode: Atmosphere independent metallic perovskite CaVxO3-δ

An alternative oxide anode material to surpass Ni electrode in the solid oxide fuel cell (SOFC) technology, used at high temperature range (500–1000 °C), is needed for the SOFC industry. We investigated an advanced perovskite oxide electrode, CaVxO3-δ system, for the alternative oxide anode material. The CaVxO3-δ powder and bulk were fabricated by using an atmosphere controlled solid-state reaction method and spark plasma sintering (SPS), respectively. The bulk specimen showed 3-3 type nonstoichiometric composite structure, and the electrical conductivity and Seebeck coefficient measurements revealed metallic n-type conductivity. Surprisingly, the high electrical conductivity (> 12,000 S/cm at room temperature; >1000 S/cm at 1000 K) was stable at different atmospheres between air and reduction atmospheres, attributing to a non-redoxable electron-cloud-channel phase protected by a redoxable protection phase. It is believed that the CaVxO3-δ system can be used as a promising and atmosphere stable oxide electrode in the fuel cell technology and other applications.

A novel composite of SnOx nanoparticles and SiO2@N-doped carbon nanofibers with durable lifespan for diffusion-controlled lithium storage

Carbon group materials, such as Si, SiO2, Sn and SnO2, with high theoretical capacity as anodes for lithium ion batteries (LIBs), suffer from the poor cycling stability resulting from the huge volume variation. To overcome the defects, a novel composite of hydrothermally synthesized ultrafine SnOx nanoparticles and SiO2@one-dimensional (1D) N-doped carbon nanofibers (SnOx/SiO2@N-CNF) is fabricated by electrospinning technique. Benefiting from the unique structure design that the SnOx and SiO2 nanoparticles are firmly encapsulated in the N-doped carbon nanofibers (N-CNFs), the SnOx/SiO2@N-CNF electrode exhibits not only excellent rate performance (434 mAh/g at 2 A/g), but also remarkable long-term cycling performance (754 mAh/g at 1 A/g after 1000 cycles) as the anode of LIBs. The N-CNFs can efficiently prevent the volume expansion and the direct contact with electrolyte of SnOx and SiO2, as well as shorten the diffusion path of lithium ions to improve the electrical conductivity. Interestingly, owing to the synergistic effect of SnOx and SiO2, the diffusion-controlled redox reaction dominates the charge transfer during charge-discharge process. As a consequence, the SnOx/SiO2@N-CNF could be a promising anode material with the extraordinary long-term cycling performance at high current densities, and provide a novel alternative anode material for LIBs quick-acting charging technology.

Strategies for the Analysis of Graphite Electrode Function

AbstractSince the commercialization of lithium‐ion batteries, graphite has been the uncontested material of choice as the negative electrode host structure, and it has therefore been pivotal for their ubiquitous adoption and implementation. Despite extensive research efforts dedicated to discovering and developing alternative anode material candidates, no commercially viable successor has so‐far been identified. Simultaneously, the understanding of graphite electrode function is continuously expanding, and new strategies for rationally improving performance are being explored. Here, the key challenges lie in examining the graphitic material, not only in the pure as‐prepared state, but also when formed into an electrode and during electrochemical cycling, i.e., in situ/operando. A multiscale approach is necessary to accurately relate the (de)lithiation/(de)intercalation mechanisms involved to the observed performance. The present review summarizes conventional techniques and highlights recent advances in the analytical methods used for the characterization of graphite‐based electrode structure and function. The discussion is based on examples from key recent work using innovative analytical strategies to obtain novel insight into the evolution in structure, microstructure, electronic structure, surface chemistry/composition, etc. The deeper understanding of material function gained from these innovative approaches may hold the key for the rational design of next‐generation graphite‐based or ‐inspired electrodes.

Second life and recycling: Energy and environmental sustainability perspectives for high-performance lithium-ion batteries.

Second life and recycling of retired automotive lithium-ion batteries (LIBs) have drawn growing attention, as large volumes of LIBs will retire in the coming decade. Here, we illustrate how battery chemistry, use, and recycling can influence the energy and environmental sustainability of LIBs. We find that LIBs with higher specific energy show better life cycle environmental performances, but their environmental benefits from second life application are less pronounced. Direct cathode recycling is found to be the most effective in reducing life cycle environmental impacts, while hydrometallurgical recycling provides limited sustainability benefits for high-performance LIBs. Battery design with less aluminum and alternative anode materials, such as silicon-based anode, could enable more sustainable LIB recycling. Compared to directly recycling LIBs after their electric vehicle use, carbon footprint and energy use of LIBs recycled after their second life can be reduced by 8 to 17% and 2 to 6%, respectively.

Electrochemical Stability of Stainless Steels-Made Alkaline Water Electrolysis Anodes Under Potential Cycle Loadings

Introduction Developing highly active and durable electrocatalysts for oxygen evolution reaction (OER) have been needed for efficient hydrogen production by alkaline water electrolysis (AWE). Austenitic stainless steels (SS) have attracted attentions as the alternative anode materials to Ni-based electrodes (1, 2). We recently demonstrated that NiFe hydroxide/oxide hetero nanostructures that synthesized through the constant current density electrolysis of 316SS (NiFe-HyOx/SS) show high OER activity and stability under constant current operation conditions (3). However, the electrochemical stability and OER overpotentials of the surface catalyst layers generated on the stainless steel under potential fluctuation is still not clear. In this study, we investigated changes in OER overpotentials of the NiFe-HyOx/SS anode during applying potential cycles (PCs) of 0.5 and 1.8 V vs. reversible hydrogen electrode (RHE) and discussed the structural changes. Experimental A 316SS plate was used as a substrate for preparing NiFe-HyOx/SS anode. The SS plate surface was polished using emery paper and alumina paste and then, washed with ultrapure water and acetone. The pre-processing SS plate surface was subsequently subjected to constant current density electrolysis of 30 mA/cm2 in 1 M KOH solution at 75 ℃ for 5 h to generate NiFe-HyOx catalyst layers (3). After that, the OER properties were examined in 7 M KOH at 20 ℃. The OER polarization curves were measured at a sweep rate of 5 mV/s. The cyclic voltammograms were collected at 50 mV/s between 0.93 and 1.49 V vs. RHE. The electrochemical stability of the samples was evaluated by applying PCs between 0.5 and 1.8 V at 1 V/s (4). Nanostructures and compositions of the surface oxide layers generated after the potential cycle loadings were investigated by scanning transmission electron microscopy (STEM) with electron dispersive spectroscopy (EDS). Results and Discussions Figs.1 (a) shows cross-sectional STEM image of the pristine NiFe-HyOx/SS sample. Fiber-like nanostructure with ca. 50 nm thickness is formed on the SS substrate, accompanied with a relatively dense, 30nm-thick buffer layer. Figs.1 (b) shows changes in OER overpotentials during the 20000 PCs of the NiFe-HyOx/SS and pure Ni samples that estimated at current density of 100 mA/cm2. The initial overpotential of the NiFe-HyOx/SS (ca. 270 mV) was lower by 110 mV than Ni (ca. 380 mV), indicating that the NiFe-HyOx/SS shows much higher initial OER activity. Polarization curves recorded before and after the 20000 PCs are shown in Figs.1 (c) and (d). The OER current densities of the NiFe-HyOx/SS are remained nearly unchanged after 20000 PCs. On the other hand, the polarization curve of the Ni shifted to positive potential side by applying the PCs, accompanying decrease in current density. The OER overpotential of the Ni sample estimated after the 20000 PCs is 480 mV, the value of which is ca. 100 mV higher compared with pristine state, indicating that the NiFe-HyOx/SS is highly stable against the PCs, relative to the Ni.To clarify the origin of high stability of the NiFe-HyOx/SS, cross-sectional STEM observations were conducted. Cross-sectional STEM images of the NiFe-HyOx/SS collected after the 20000 PCs are summarized in Figs.1 (e) and (f). As can be seen in (e), the total thickness of the surface catalyst and PCs-generated interlayers was estimated to be ca. 900 nm in thickness. The magnified image of the topmost surface regions (f) shows the 50nm-thick catalyst layer at pristine state (Figs. 1(a)) keeps its thickness and nanofiber-like structure even after the 20000 PCs. On the other hand, the buffer layer between the surface catalyst layer and SS substrate grown by the PCs loading, resulting in ca. 850nm-thick interlayer. The XPS and STEM-EDS analysis results (not shown) showed initial surface chemical compositions (Ni:Fe = 1:1) of the catalyst layer almost retained after the 20000 PCs, indicating that the surface catalyst nanofiber-like structures which is electrochemically stable against the PCs loading should contribute to the stable OER property of the NiFe-HyOx/SS anode (5).AcknowledgmentsThis study was partly supported by JSPS KAKENHI Grant Number 18H01741 and 21H01661, Toyota Mobility Foundation Hydrogen Initiative, and Advanced Research and Education Center for Steel (ARECS). References H. Schäfer and M. Chatenet, ACS Energy Lett., 3, 574 (2018). F. Moureaux, P. Stevens, G. Toussaint and M. Chatenet, Appl. Catal., B, 258, 117963 (2019). N. Todoroki and T. Wadayama, ACS Appl. Mater., 11, 44161 (2019). S. Fujita, I. Nagashima, Y. Nishiki, C. Canaff, T. W. Napporn and S. Mitsushima, Electrocatalysis, 9, 162 (2018). N. Todoroki and T. Wadayama, Electrochem. Commun., 122, 106902 (2021). Figure 1

Nanostructured Sn–Mo multilayer film anode with stable electrode-interfaces for long-cycle lithium storage

Sn has emerged as an alternative anode material which involves alloying reactions toward Li storage. However, its huge volume and structural changes lead to severe degradation of the electrode and cumulative thickening of the solid electrolyte interface (SEI) upon cycling, which dramatically shorten the cycle life of the electrode. Here, we demonstrate that in the rationally designed interface structure of Sn–Mo film electrodes, with the addition of Mo protective layers and the well-dispersed dot-like Mo nanoparticles in the Sn–Mo layer, the highly stable electrode-interfaces and improved electrochemical performance can be achieved. The Mo/Sn–Mo/Mo multilayered electrode exhibits an initial reversible capacity of 870 mA h g−1, and maintains a capacity retention of 70% after 400 cycles between 0.01 and 2 V vs. Li/Li+, much superior to those previous reported Sn-based alloy thin film anodes. Besides, the Mo/Sn–Mo/Mo electrode can achieve 540 mA h g−1 after 200 cycles within 0.01–1.2 V on both copper foil and carbon film current collectors, and has superior stable reversible capacities within 0.2–1.2 V and 0.01–0.8 V. This work based on interfacial modification provides a fundamental strategy to design electrode materials for large capacity and flexible lithium-ion batteries.

Anode processes on Pt and ceramic anodes in chloride and oxide-chloride melts

Platinum anodes are widely used for metal oxides reduction in LiCl–Li2O, however high-cost and low-corrosion resistance hinder their implementation. NiO–Li2O ceramics is an alternative corrosion resistant anode material. Anode processes on platinum and NiO–Li2O ceramics were studied in (80 mol.%)LiCl-(20mol.%)KCl and (80 mol.%)LiCl-(20 mol.%)KCl–Li2O melts by cyclic voltammetry, potentiostatic and galvanostatic electrolysis. Experiments performed in the LiCl–KCl melt without Li2O illustrate that a Pt anode dissolution causes the Pt2+ ions formation at 3.14 V and 550°С and at 3.04 V and 650оС. A two-stage Pt oxidation was observed in the melts with the Li2O at 2.40 ÷ 2.43 V, which resulted in the Li2PtO3 formation. Oxygen current efficiency of the Pt anode at 2.8 V and 650°С reached about 96%. The anode process on the NiO–Li2O electrode in the LiCl–KCl melt without Li2O proceeds at the potentials more positive than 3.1 V and results in the electrochemical decomposition of ceramic electrode to NiO and O2. Oxygen current efficiency on NiO–Li2O is close to 100%. The NiO–Li2O ceramic anode demonstrated good electrochemical characteristics during the galvanostatic electrolysis at 0.25 A/cm2 for 35 h and may be successfully used for pyrochemical treating of spent nuclear fuel.

Electrochemical Characteristics of Synthesized Nb 2 O 5 -Li 3 VO 4 Composites as Li Storage Materials

The increasing demand for energy storage in mobile electronic devices and electric vehicles has emphasized the importance of electrochemical energy storage devices such as Li-ion batteries (LIBs) and supercapacitors. For reversible Li storage, alternative anode materials are actively being developed. In this study, we designed and fabricated an Nb2O5-Li3VO4 composite for use as an anode material in LIBs and hybrid supercapacitors. Nb2O5 powders were dissolved into a solution and the precursors were precipitated onto Li3VO4 through a simple, low-temperature hydrothermal reaction. The annealing process yielded an Nb2O5-Li3VO4 composite that was characterized by X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy. Electrochemical tests revealed that the Nb2O5-Li3VO4 composite electrode demonstrated increased capacities of approximately 350 and 140 mAh g-1 at 0.1 and 5 C, respectively, were maintained up to 1000 cycles. The reversible capacity and rate capability of the composite electrode were enhanced compared to those of pure Nb2O5-based electrodes. These results can be attributed to the microstructure design of the synthesized composite material.

Phase structure engineering of MnCo2Ox within electrospun carbon nanofibers towards high-performance lithium-ion batteries

Metal oxides are prospective alternative anode materials to the commercial graphite for lithium ion batteries (LIBs), while their practical application is seriously hampered by their poor conductivities and large volume changes. Herein, we report the controllable synthesis of amorphous/crystalline MnCo2Ox nanoparticles within porous carbon nanofibers (marked as MCO@CNFs) through a facile electrospinning strategy and subsequent annealing reactions. The phase structures from Co/MnOX to amorphous MnCo2Ox and crystalline MnCo2O4.5 can be readily tuned by thermal reduction/oxidation under controlled atmosphere and temperature. When examined as anode for LIBs, the optimized MCO@CNFs delivers a high stable capacity of 780.3 mA h g−1 at 200 mA g−1 after 250 cycles, which is attributed to the synergistic effect of the distinctive amorphous structure and defective carbon nanofiber matrices. Specifically, the amorphous structure with rich defects offers more reactive sites and multiple pathways for the Li+ diffusion, while carbon hybridization sufficiently improves the electrode conductivities as well as buffers the volume changes. More importantly, we demonstrate a convenient synthesis strategy to control the metal-to-oxide structure evolution within carbon matrices, which is of great importance in exploring high-performance electrodes for next generation LIBs.

Effect of rGO loading on the electrochemical performance of Li 22 Si 5 / rGO composite anodes for lithium‐ion batteries

In this work, as an alternative to the silicon-based anodes, Li22Si5/rGO composite electrodes were synthesized and their electrochemical performances were investigated by the electrochemical impedance spectroscopy, cyclic voltammetry, and charge/discharge tests. The effects of rGO and PVDF contents on the performance of the composite electrodes were also observed. Although the composite electrodes with the low PVDF content exhibited a high discharge capacity, their cyclic performances were very poor. The excess amount of PVDF content, however, even in the presence of high rGO content, caused the charge transfer resistance and the discharge capacity irreversibility to increase in the composite electrodes. The composite electrode with 70% Li22Si5 alloy, 15% rGO, and 15% PVDF (LSRGO15) contents exhibited the best electrode performance in this work. The LSRGO15 electrode had 822 mA h g−1 discharge capacity at the 100th cycle. These performance values demonstrated that Li22Si5/rGO composite electrodes were highly promising as the alternative anode materials for the LIBs.

Strontium Stannate as an Alternative Anode Material for Li-Ion Batteries

Strontium Stannate as an Alternative Anode Material for Li-Ion Batteries

The Potassium–Air Battery: Far from a Practical Reality?

ConspectusAn energy storage system is the key bottleneck toward the widespread use of renewable energy and the development of electric vehicles (EVs). Alkali metal–oxygen batteries, which have higher gravimetric energy densities (3500–935 Wh kg–1) than conventional lithium–ion batteries (100–265 Wh kg–1), are considered to be one of the promising next-generation energy storage systems. Over the past decade, Li–O2 batteries have been the center of the research effort owing to their highest energy density. However, the poor reversibility, low round-trip efficiency, and limited cycle life originating from sluggish kinetic and serious parasitic chemistry induced by singlet oxygen hamper the development of Li–O2 batteries. Both the sluggish kinetics and severe parasitic reactions are closely related to the discharge product Li2O2. Unlike Li–O2 batteries, K–O2 batteries based on potassium superoxide offer an attractive theoretical energy density (935 Wh kg–1) with a significantly improved energy efficiency and lifetime compared to other alkali metal–O2 batteries. The fast and reversible O2/KO2 single–electron reaction exhibits higher redox kinetics compared to the Li–O2 redox chemistries and removes the needs of catalysts or redox mediators. In addition, the earth abundant K greatly alleviates the global shortage and uneven regional distribution of Li. These unique advantages of the K–O2 system make it a promising candidate for low-cost and large-scale energy storage. However, the development of a K–O2 battery is still in its early stages and its round-trip efficiency is still lower than that of lithium–ion batteries. Further improvement in energy efficiency and cycle life of the K–O2 batteries is crucial prior to practical applications. The present Account combines our efforts and other representative works on fundamental understandings and design strategies toward next-generation K–O2 batteries. Insights are offered on oxygen electrode reversibility and stability, anode stabilization and alternative anodes, and the closed system based on KO2–K2O2 conversion. Five physicochemical factors that affect the oxygen electrode reversibility and stability are discussed in light of recent findings, including electrolyte design, growth mechanism, operation environment, degradation mechanism, and electrode–electrolyte design. Furthermore, the alternative anode materials development to solve the long-standing potassium anode issue are discussed and the pros and cons of alternative anodes are compared. In addition, due to oxygen crossover to the anode and the electrolyte evaporation problem in open K–air battery systems, the feasibility and strategies to develop closed systems are briefly discussed. At the end of the Account, future directions in deepening understanding of K–O2 reaction and battery design to realize practical applications of K–O2 systems are highlighted.

Orthorhombic Y0.95-xSrxCo0.3Fe0.7O3-δ anode for oxygen evolution reaction in solid oxide electrolysis cells

Cubic perovskite oxides usually suffer from delamination and Sr2+ segregation for catalyzing oxygen evolution reaction (OER) at the anodes of solid oxide electrolysis cells (SOECs). It is crucial to develop alternative and efficient anode materials for SOECs. Herein, a series of novel Y0.95-xSrxCo0.3Fe0.7O3-δ (YSCF-x) orthorhombic perovskite oxides in the Pnma (62) space group are synthesized as anode materials of SOECs. Physicochemical characterizations and density functional theory calculations reveal that the partial substitution of Y3+ by Sr2+ increases the oxygen vacancy concentration and mobility as well as improves the electrical conductivity, which contributes to the excellent OER activity of YSCF-x. At 800 °C, the current density of SOEC with YSCF-0.05-Ce0.8Sm0.2O2-δ anode can reach 1.32 A cm−2 at 1.6 V, about twice that of SOEC with Y0.95Co0.3Fe0.7O3-δ-Ce0.8Sm0.2O2-δ anode. This work paves a new avenue for the design of advanced anode materials of SOECs.

A novel synthetic strategy towards NaCl-type NixCo1−xO solid solution nanoplatelets encapsulated in N-doped carbon for enhanced lithium-ion storage

NaCl-type Ni-Co oxide solid solution is expected to be a promising alternative anode material for lithium-ion batteries. However, the synthesis of solid solutions with well-defined morphology and homogeneity is still challenging. Based on a novel NixCo1−x(OH)(OCH3)@polydopamine intermediate and its topotactic thermolysis, a unique synthetic route towards NixCo1−xO solid solution (0 <x ≤ 0.5) encapsulated in N-doped carbon (NixCo1−xO@N-C) was introduced. NixCo1−x(OH)(OCH3) nanoplatelets were firstly synthesized with a solvothermal method and used as the precursor for a NixCo1−x(OH)(OCH3)@polydopamine intermediate. Thermolytic decomposition of metastable NixCo1−x(OH)(OCH3)@polydopamine results in the formation of NaCl-type NixCo1−xO and conformal carbon coating. The resulting NixCo1−xO@N-C shows a well-defined two-dimensional (2D) platelet-morphology and homogenous elemental distribution. Benefited from a tunable Ni/Co ratio, the lithium-storage performance of NixCo1−xO@N-C can be optimized, thereby achieving a high specific capacity of 949 mA h g−1 at the current density of 0.2 A g−1, a great rate capability (530 mA h g−1 at 2 A g−1), as well as excellent long-term cyclability (563 mA h g−1 at 2 A g−1 after 500 cycles) for Ni1/6Co5/6O@N-C. Such a remarkable performance could be attributed to the synergistic effect of different cations, the 2D nanoplatelet structure, the robust conductive carbon coating, and a high pseudocapacitive contribution.