Abstract: Silicon oxides have been recognized as a promising family of anode materials for high-energy lithium-ion batteries (LIBs) owing to their abundant reserve, low cost, environmental friendliness, easy synthesis, and high theoretical capacity. However, the extended application of silicon oxides is severely hampered by the intrinsically low conductivity, large volume change, and low initial coulombic efficiency. Significant efforts have been dedicated to tackling these challenges towards practical applications. This Review focuses on the recent advances in the synthesis and lithium storage properties of silicon oxide-based anode materials. To present the progress in a systematic manner, this review is categorized as follows: (i) SiO-based anode materials, (ii) SiO2-based anode materials, (iii) non-stoichiometric SiOx-based anode materials, and (iv) Si-O-C-based anode materials. Finally, future outlook and our personal perspectives on silicon oxide-based anode materials are presented.

Abstract: Cells with lithium-metal anodes are viewed as the most viable future technology, with higher energy density than existing lithium-ion batteries. Many researchers believe that for lithium-metal cells, the typical liquid electrolyte used in lithium-ion batteries must be replaced with a solid-state electrolyte to maintain the flat, dendrite-free lithium morphologies necessary for long-term stable cycling. Here, we show that anode-free lithium-metal pouch cells with a dual-salt LiDFOB/LiBF4 liquid electrolyte have 80% capacity remaining after 90 charge–discharge cycles, which is the longest life demonstrated to date for cells with zero excess lithium. The liquid electrolyte enables smooth dendrite-free lithium morphology comprised of densely packed columns even after 50 charge–discharge cycles. NMR measurements reveal that the electrolyte salts responsible for the excellent lithium morphology are slowly consumed during cycling. Extensive efforts have recently been geared towards developing all-solid-state batteries largely because of their potential to enable high-energy-density Li anodes. Here, the authors report a high-performance lithium pouch cell with no excess lithium, enabled by just a dual-salt liquid electrolyte.

Abstract: Rechargeable aqueous zinc-ion batteries have been considered as a promising candidate for next-generation batteries. However, the formation of zinc dendrites are the most severe problems limiting their practical applications. To develop stable zinc metal anodes, a synergistic method is presented that combines the Cu-Zn solid solution interface on a copper mesh skeleton with good zinc affinity and a polyacrylamide electrolyte additive to modify the zinc anode, which can greatly reduce the overpotential of the zinc nucleation and increase the stability of zinc deposition. The as-prepared zinc anodes show a dendrite-free plating/stripping behavior over a wide range of current densities. The symmetric cell using this dendrite-free anode can be cycled for more than 280 h with a very low voltage hysteresis (93.1 mV) at a discharge depth of 80 %. The high capacity retention and low polarization are also realized in Zn/MnO2 full cells.

Abstract: Aqueous K-ion batteries (AKIBs) are promising candidates for grid-scale energy storage due to their inherent safety and low cost. However, full AKIBs have not yet been reported due to the limited availability of suitable electrodes and electrolytes. Here we propose an AKIB system consisting of an Fe-substituted Mn-rich Prussian blue KxFeyMn1 − y[Fe(CN)6]w·zH2O cathode, an organic 3,4,9,10-perylenetetracarboxylic diimide anode and a 22 M KCF3SO3 water-in-salt electrolyte. The cathode achieves 70% capacity retention at 100 C and a lifespan of over 10,000 cycles due to the mitigation of phase transitions by Fe substitution. Meanwhile, the electrolyte can help decrease the dissolution of both electrodes owing to the lack of free water. The AKIB exhibits a high energy density of 80 Wh kg−1 and can operate well at rates of 0.1–20 C and over a wide temperature range (−20 to 60 °C). We believe that our demonstration could pave the way for practical applications of AKIBs for grid-scale energy storage. Intensive efforts are underway towards developing battery-based grid-scale storage technologies. Here, the authors report an aqueous K-ion battery that offers many attractive advantages over various battery alternatives.

Abstract: A critical current density on stripping is identified that results in dendrite formation on plating and cell failure. When the stripping current density removes Li from the interface faster than it can be replenished, voids form in the Li at the interface and accumulate on cycling, increasing the local current density at the interface and ultimately leading to dendrite formation on plating, short circuit and cell death. This occurs even when the overall current density is considerably below the threshold for dendrite formation on plating. For the Li/Li6PS5Cl/Li cell, this is 0.2 and 1.0 mA cm−2 at 3 and 7 MPa pressure, respectively, compared with a critical current for plating of 2.0 mA cm−2 at both 3 and 7 MPa. The pressure dependence on stripping indicates that creep rather than Li diffusion is the dominant mechanism transporting Li to the interface. The critical stripping current is a major factor limiting the power density of Li anode solid-state cells. Considerable pressure may be required to achieve even modest power densities in solid-state cells. A ceramic electrolyte with a lithium metal anode can offer advantages over liquid electrolytes for Li-ion battery performance. A critical current density on stripping in a solid-state cell is identified, resulting in dendrite formation on plating and failure.

Abstract: The surface chemistry of solid electrolyte interphase is one of the critical factors that govern the cycling life of rechargeable batteries. However, this chemistry is less explored for zinc anodes, owing to their relatively high redox potential and limited choices in electrolyte. Here, we report the observation of a zinc fluoride-rich organic/inorganic hybrid solid electrolyte interphase on zinc anode, based on an acetamide-Zn(TFSI)2 eutectic electrolyte. A combination of experimental and modeling investigations reveals that the presence of anion-complexing zinc species with markedly lowered decomposition energies contributes to the in situ formation of an interphase. The as-protected anode enables reversible (~100% Coulombic efficiency) and dendrite-free zinc plating/stripping even at high areal capacities (>2.5 mAh cm‒2), endowed by the fast ion migration coupled with high mechanical strength of the protective interphase. With this interphasial design the assembled zinc batteries exhibit excellent cycling stability with negligible capacity loss at both low and high rates. Zinc chemistry is not favourable to the formation of a solid electrolyte interphase as a result of its high redox potential. In a break with the traditional wisdom, the present authors realise ZnF2-rich hybrid SEI on Zn anode via the modulation of cationic speciation in a eutectic electrolyte.

Abstract: Electrolysis of water to generate hydrogen fuel is an attractive renewable energy storage technology. However, grid-scale freshwater electrolysis would put a heavy strain on vital water resources. Developing cheap electrocatalysts and electrodes that can sustain seawater splitting without chloride corrosion could address the water scarcity issue. Here we present a multilayer anode consisting of a nickel–iron hydroxide (NiFe) electrocatalyst layer uniformly coated on a nickel sulfide (NiSx) layer formed on porous Ni foam (NiFe/NiSx-Ni), affording superior catalytic activity and corrosion resistance in solar-driven alkaline seawater electrolysis operating at industrially required current densities (0.4 to 1 A/cm2) over 1,000 h. A continuous, highly oxygen evolution reaction-active NiFe electrocatalyst layer drawing anodic currents toward water oxidation and an in situ-generated polyatomic sulfate and carbonate-rich passivating layers formed in the anode are responsible for chloride repelling and superior corrosion resistance of the salty-water-splitting anode.

Abstract: Graphite as an anode for the potassium ion battery (PIBs) has the merits of low cost and potentially high energy density, while suffering from limited cycle time and inferior stability. Herein we, using a concentrated electrolyte, demonstrate that formation of a robust inorganic-rich passivation layer on the graphite anode could resolve these problems. Consequently, the PIBs with graphite anode could operate for over 2000 cycles (running time of over 17 months) with negligible capacity decay, and had a high area capacity over 7.36 mAh cm-2 with a high mass loading of 28.56 mg cm-2 . These unprecedented performances of graphite are comparable to that of traditional lithium-ion batteries, and may promote the rapidly development of high performance PIBs.

Abstract: Although silicon is a promising anode material for lithium-ion batteries, scalable synthesis of silicon anodes with good cyclability and low electrode swelling remains a significant challenge. Herein, we report a scalable top-down technique to produce ant-nest-like porous silicon from magnesium-silicon alloy. The ant-nest-like porous silicon comprising three-dimensional interconnected silicon nanoligaments and bicontinuous nanopores can prevent pulverization and accommodate volume expansion during cycling resulting in negligible particle-level outward expansion. The carbon-coated porous silicon anode delivers a high capacity of 1,271 mAh g−1 at 2,100 mA g−1 with 90% capacity retention after 1,000 cycles and has a low electrode swelling of 17.8% at a high areal capacity of 5.1 mAh cm−2. The full cell with the prelithiated silicon anode and Li(Ni1/3Co1/3Mn1/3)O2 cathode boasts a high energy density of 502 Wh Kg−1 and 84% capacity retention after 400 cycles. This work provides insights into the rational design of alloy anodes for high-energy batteries. Silicon is a promising anode material for lithium-ion batteries but experiences large volume changes during cycling. Here the authors report a scalable method to synthesize porous ant-nest-like silicons. The unique structure of this anode solves the swelling problem and enables impressive performance.

Abstract: Lithium metal anodes have attracted much attention as candidates for high-energy batteries, but there have been few reports of long cycling behaviour, and the degradation mechanism of realistic high-energy Li metal cells remains unclear. Here, we develop a prototypical 300 Wh kg−1 (1.0 Ah) pouch cell by integrating a Li metal anode, a LiNi0.6Mn0.2Co0.2O2 cathode and a compatible electrolyte. Under small uniform external pressure, the cell undergoes 200 cycles with 86% capacity retention and 83% energy retention. In the initial 50 cycles, flat Li foil converts into large Li particles that are entangled in the solid-electrolyte interphase, which leads to rapid volume expansion of the anode (cell thickening of 48%). As cycling continues, the external pressure helps the Li anode maintain good contact between the Li particles, which ensures a conducting percolation pathway for both ions and electrons, and thus the electrochemical reactions continue to occur. Accordingly, the solid Li particles evolve into a porous structure, which manifests in substantially reduced cell swelling by 19% in the subsequent 150 cycles. Much has been said about the high-energy, long-lasting potential of Li metal batteries, and yet little has been demonstrated at the cell scale. Here, Jun Liu and colleagues demonstrate a Li metal pouch cell with a 300 Wh kg−1 energy density and a 200-cycle lifetime.

Abstract: Summary It has been a long pursuit for the adoption of the lithium (Li) metal anode because of its extremely high specific capacity and the lowest electrochemical equilibrium potential. However, the practical implement of Li anode is severely hindered by the unstable interfaces stemming from its ultrahigh reactivity, which directly dictates a low Coulombic efficiency, dendrite growth behavior, and even safety concerns. In this review, we focus on the emerging strategy of artificial protective films to fulfill a stable working Li metal anode. The recent efforts on strengthening the Li metal and liquid or solid electrolyte interfaces with artificial films are comprehensively summarized and discussed. This review highlights the significance of interface-related science and engineering in both liquid-state and solid-state Li metal batteries, affords fresh insights on the interdisciplinary issues, and calls on more dedication to pave the way for safe and high-energy-density Li metal batteries.

Abstract: For the development of next-generation lithium batteries, major research effort is made to enable a reversible lithium metal anode by the use of solid electrolytes. However, the fundamentals of the solid-solid interface and especially the processes that take place under current load are still not well characterized. By measuring pressure-dependent electrode kinetics, we explore the electrochemo-mechanical behavior of the lithium metal anode on the garnet electrolyte Li6.25Al0.25La3Zr2O12. Because of the stability against reduction in contact with the lithium metal, this serves as an optimal model system for kinetic studies without electrolyte degradation. We show that the interfacial resistance becomes negligibly small and converges to practically 0 Ω·cm2 at high external pressures of several 100 MPa. To the best of our knowledge, this is the smallest reported interfacial resistance in the literature without the need for any interlayer. We interpret this observation by the concept of constriction resistance and show that the contact geometry in combination with the ionic transport in the solid electrolyte dominates the interfacial contributions for a clean interface in equilibrium. Furthermore, we show that-under anodic operating conditions-the vacancy diffusion limitation in the lithium metal restricts the rate capability of the lithium metal anode because of contact loss caused by vacancy accumulation and the resulting pore formation near the interface. Results of a kinetic model show that the interface remains morphologically stable only when the anodic load does not exceed a critical value of approximately 100 μA·cm-2, which is not high enough for practical cell setups employing a planar geometry. We highlight that future research on lithium metal anodes on solid electrolytes needs to focus on the transport within and the morphological instability of the metal electrode. Overall, the results help to develop a deeper understanding of the lithium metal anode on solid electrolytes, and the major conclusions are not limited to the Li|Li6.25Al0.25La3Zr2O12 interface.

Abstract: Industrially profitable water splitting is one of the great challenges in the development of a viable and sustainable hydrogen economy. Alkaline electrolysers using Earth-abundant catalysts remain the most economically viable route to electrolytic hydrogen, but improved efficiency is desirable. Recently, electron spin polarization was described as a potential way to improve water-splitting catalysis. Here, we report the significant enhancement of alkaline water electrolysis when a moderate magnetic field (≤450 mT) is applied to the anode. Current density increments above 100% (over 100 mA cm−2) were found for highly magnetic electrocatalysts, such as the mixed oxide NiZnFe4Ox. Magnetic enhancement works even for decorated Ni–foam electrodes with very high current densities, improving their intrinsic activity by about 40% to reach over 1 A cm−2 at low overpotentials. Thanks to its simplicity, our discovery opens opportunities for implementing magnetic enhancement in water splitting. Some of the best electrocatalysts for the oxygen evolution reaction in alkaline electrolysers are based on oxides of nickel and iron. Here, the authors demonstrate that the water oxidation performance of such catalysts can be enhanced by application of a magnetic field from a permanent magnet.

Abstract: The stability of a battery is strongly dependent on the feature of solid electrolyte interphase (SEI). The electrical double layer forms prior to the formation of SEI at the interface between the Li metal anode and the electrolyte. The fundamental understanding on the regulation of the SEI structure and stability on Li surface through the structure of the electrical double layer is highly necessary for safe batteries. Herein, the interfacial chemistry of the SEI is correlated with the initial Li surface adsorption electrical double layer at the nanoscale through theoretical and experimental analysis. Under the premise of the constant solvation sheath structure of Li+ in bulk electrolyte, a trace amount of lithium nitrate (LiNO3) and copper fluoride (CuF2) were employed in electrolytes to build robust electric double layer structures on a Li metal surface. The distinct results were achieved with the initial competitive adsorption of bis(fluorosulfonyl)imide ion (FSI-), fluoride ion (F-), and nitrate ion (NO3-) in the inner Helmholtz plane. As a result, Cu-NO3- complexes are preferentially adsorbed and reduced to form the SEI. The modified Li metal electrode can achieve an average Coulombic efficiency of 99.5% over 500 cycles, enabling a long lifespan and high capacity retention of practical rechargeable batteries. The as-proposed mechanism bridges the gap between Li+ solvation and the adsorption about the electrode interface formation in a working battery.

Abstract: Despite considerable efforts to stabilize lithium metal anode structures and prevent dendrite formation, achieving long cycling life in high-energy batteries under realistic conditions remains extremely difficult due to a combination of complex failure modes that involve accelerated anode degradation and the depletion of electrolyte and lithium metal. Here we report a self-smoothing lithium–carbon anode structure based on mesoporous carbon nanofibres, which, coupled with a lithium nickel–manganese–cobalt oxide cathode with a high nickel content, can lead to a cell-level energy density of 350–380 Wh kg−1 (counting all the active and inactive components) and a stable cycling life up to 200 cycles. These performances are achieved under the realistic conditions required for practical high-energy rechargeable lithium metal batteries: cathode loading ≥4.0 mAh cm−2, negative to positive electrode capacity ratio ≤2 and electrolyte weight to cathode capacity ratio ≤3 g Ah−1. The high stability of our anode is due to the amine functionalization and the mesoporous carbon structures that favour smooth lithium deposition. Metallic lithium wets a functionalized mesoporous carbon film to create a self-smoothing anode that, in conjunction with a standard lithium nickel–manganese–cobalt cathode, delivers long cycling life, 350 Wh kg−1 high-energy cells under realistic conditions.

Abstract: Dendrite growth of metal anodes is one of the key hindrances for both secondary aqueous metal batteries and nonaqueous metal batteries. In this work, a freestanding Ti3C2Tx MXene@Zn paper is designed as both zinc metal anode and lithium metal anode host to address the issue. The binder-free Ti3C2Tx MXene@Zn paper exhibits merits of good mechanical flexibility, high electronic conductivity, hydrophilicity, and lithiophilicity. The crystal growth mechanism of Zn metal on common Zn foil and Ti3C2Tx MXene@Zn composite is also studied. It is found that the Ti3C2Tx MXene@Zn paper can effectively suppress the dendrite growth of Zn, enabling reversible and fast Zn plating/stripping kinetics in an aqueous electrolyte. Moreover, the Ti3C2Tx MXene@Zn paper can be used as a 3D host for a lithium metal anode. In this host, Zn is utilized as a nucleation agent to suppress the Li dendrite growth. The freestanding Ti3C2Tx MXene@Zn@Li anode exhibits superior reversibility with high Coulombic efficiency (97.69% over 600 cycles at 1.0 mA cm-2) and low polarization compared with the Cu@Li anode. These findings may be useful for the design of dendrite-free metal-based energy storage systems.

Abstract: Zinc ion batteries (ZIBs) have attracted extensive attention in recent years, benefiting from their high safety, eco-friendliness, low cost, and high energy density. Although many cathode materials for ZIBs have been developed, the poor stability of zinc anodes caused by uneven deposition/stripping of zinc has inevitably limited the practical application of ZIBs. Herein, we report a highly stable 3D Zn anode prepared by electrodepositing Zn on a chemically etched porous copper skeleton. The inherent excellent electrical conductivity and open structure of the 3D porous copper skeleton ensure the uniform deposition/stripping of Zn. The 3D Zn anode exhibits reduced polarization, stable cycling performance, and almost 100% Coulombic efficiency as well as fast electrochemical kinetics during repeated Zn deposition/stripping processes for 350 h. Furthermore, full cells with a 3D Zn anode, ultrathin MnO2 nanosheet cathode, and Zn2+-containing aqueous electrolyte delivered a record-high capacity of 364 mAh g–1 at...

Abstract: Hydrogen production by electrocatalytic water splitting is an efficient and economical technology, however, is severely impeded by the kinetic-sluggish and low value-added anodic oxygen evolution reaction. Here we report the nickel-molybdenum-nitride nanoplates loaded on carbon fiber cloth (Ni-Mo-N/CFC), for the concurrent electrolytic productions of high-purity hydrogen at the cathode and value-added formate at the anode in low-cost alkaline glycerol solutions. Especially, when equipped with Ni-Mo-N/CFC at both anode and cathode, the established electrolyzer requires as low as 1.36 V of cell voltage to achieve 10 mA cm−2, which is 260 mV lower than that in alkaline aqueous solution. Moreover, high Faraday efficiencies of 99.7% for H2 evolution and 95.0% for formate production have been obtained. Based on the excellent electrochemical performances of Ni-Mo-N/CFC, electrolytic H2 and formate productions from the alkaline glycerol solutions are an energy-efficient and promising technology for the renewable and clean energy supply in the future. Hydrogen production by electrocatalytic water splitting is limited by the sluggish evolution kinetics of low value-oxygen. Here, authors show concurrent electrolytic productions of H2 and glycerol oxidation to formate by utilizing Ni-Mo-N/CFC electro-catalyst as both anodic and cathodic catalysts.

Abstract: Developing inexpensive and efficient electrocatalysts for hydrogen evolution reaction (HER) during alkaline water electrolysis is crucial for renewable and sustainable energy harvesting. Herein, we report a novel hybrid electrocatalyst comprising atomically dispersed Ni–Nx species anchored porous carbon (Ni–N–C) matrix with embedded Ni nanoparticles for HER. This new catalyst is synthesized via pyrolysis of hydrothermally prepared supermolecular composite of dicyandiamide and Ni ions followed by an acid etching treatment. The achieved hybrid exhibits superior catalytic performance toward HER with a small overpotential of 147 mV at 10 mA cm−2 and a low Tafel slope of 114 mV dec−1, comparable to those of state-of-the-art heteroatom-doped nanocarbon catalysts and even outperforming other reported transition-metal-based compounds in basic media. Experimental observations and theoretical calculations reveal that the presence of Ni nanoparticles can optimize surface states of Ni−Nx active centers and reduce energy barriers of dissociated water molecules, which synergistically improve OH− adsorption and promote HER kinetics. When served as electrodes for both cathode and anode, an alkaline water electrolyzer could afford a current density of 10 mA cm−2 at a low cell voltage of 1.58 V, rivalling the sufficiently high overpotentials of integrated Pt/C–Ir/C benchmark electrodes.

Abstract: No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite-free plating of a lithium-metal anode and a Li+ extraction from an oxide host cathode without electrolyte oxidation in a high-voltage cell during the charge process. Therefore, a double-layer polymer electrolyte is investigated, in which one polymer provides dendrite-free plating of a Li-metal anode and the other allows a Li+ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium-metal anode and a poly(N-methyl-malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li+ conductivity on crossing the polymer/polymer interface.

Abstract: Heteroatom-doped carbon materials with expanded interlayer distance have been widely studied as anodes for sodium-ion batteries (SIBs). However, it remains unexplored to further enlarge the interlayer spacing and reveal the influence of heteroatom doping on carbon nanostructures for developing more efficient SIB anode materials. Here, a series of N-rich few-layer graphene (N-FLG) with tuneable interlayer distance ranging from 0.45 to 0.51 nm is successfully synthesized by annealing graphitic carbon nitride (g-C3 N4 ) under zinc catalysis and selected temperature (T = 700, 800, and 900 °C). More significantly, the correlation between N dopants and interlayer distance of resultant N-FLG-T highlights the effect of pyrrolic N on the enlargement of graphene interlayer spacing, due to its stronger electrostatic repulsion. As a consequence, N-FLG-800 achieves the optimal properties in terms of interlayer spacing, nitrogen configuration and electronic conductivity. When used as an anode for SIBs, N-FLG-800 shows remarkable Na+ storage performance with ultrahigh rate capability (56.6 mAh g-1 at 40 A g-1 ) and excellent long-term stability (211.3 mAh g-1 at 0.5 A g-1 after 2000 cycles), demonstrating the effectiveness of material design.