High-Safety Lithium-Ion Batteries with Silicon-Based Anodes Enabled by Electrolyte Design.

High-energy-density lithium-ion batteries (LIBs) with high safety have long been pursued for extending the cruise range of electric vehicles. Owing to the high gravimetric capacity, silicon is a promising alternative to the convention graphite anode for high-energy LIBs. However, it suffers from intrinsic poor interfacial stability with liquid electrolytes, inevitably increasing the risk of thermal runaway and posing serious safety challenges. In this review, we will focus on mitigating thermal runaway of silicon anodes-based LIBs from the perspective of electrolyte design. First, the thermal runaway mechanism of LIBs is briefly introduced, while the specific thermal failure reactions associated with silicon anodes and electrolytes are discussed in detail. We then summarize the safety countermeasures (e. g., thermally stable solid electrolyte interphase, nonflammable electrolytes, highly stable lithium salts, mitigating electrode crosstalk, and solid-state electrolytes) enabled by customized electrolyte design to address these triggers of thermal runaway. Finally, the remaining unanswered questions regarding the thermal runaway mechanism are presented, and future directions to achieve intrinsically safe electrolytes for silicon-based anodes are prospected. This review is expected to provide insightful knowledge for improving the safety of LIBs with silicon-based anodes.

A Safer High-Energy Lithium-Ion Capacitor Using Fast-Charging and Stable ω-Li3 V2 O5 Anode.

Lithium-ion capacitors (LICs) are flourishing toward high energy density and high safety, which depend significantly on the performance of the intercalation-type anodes used in LICs. However, commercially available graphite and Li4 Ti5 O12 anodes in LICs suffer from inferior electrochemical performance and safety risks due to limited rate capability, energy density, thermal decomposition, and gassing issues. Here a safer high-energy LIC based on a fast-charging ω-Li3 V2 O5 (ω-LVO) anode with a stable bulk/interface structure is reported. The electrochemical performance, thermal safety, and gassing behavior of the ω-LVO-based LIC device are investigated, followed by the exploration of the stability of the ω-LVO anode. The ω-LVO anode exhibits fast lithium-ion transport kinetics at room/elevated temperatures. Paired with an active carbon (AC) cathode, the AC||ω-LVO LIC with high energy density and long-term endurability is achieved. The accelerating rate calorimetry, in situ gas assessment, and ultrasonic scanning imaging technologies further verify the high safety of the as-fabricated LIC device. Theoretical and experimental results unveil that the high safety originates from the high structure/interface stability of the ω-LVO anode. This work provides important insights into electrochemical/thermochemical behaviors of ω-LVO-based anodes within LICs and offers new opportunities to develop safer high-energy LIC devices.

Hybrid Ionogel Electrolytes for Advanced Lithium Secondary Batteries: Developments and Challenges.

Incidents in the use of lithium-ion batteries are usually caused by the malfunction of flammable organic liquid electrolytes with poor thermal stability. Therefore, the development of noncombustible electrolytes is regarded as one of the most effective means to prevent the safety hazards of lithium-ion batteries. Ionic liquids have attracted much interest recently, mainly due to their high ionic conductivity, low volatility, and incombustibility. The application of ionic liquids to the preparation of quasi-solid-state gel electrolytes combines the advantages of ionic liquids and avoids the risks of organic liquid electrolytes. Therefore, the solid-state ionogels have been considered as a promising alternative electrolyte system, especially for the much-desired energy storage devices with higher energy density and flexibility. This review focuses on the recent progress of ionogel electrolytes for lithium-ion batteries. The preparation strategies for ionogel electrolytes based on different frameworks, namely inorganic matrix, organic matrix, and organic-inorganic hybrid matrix, are discussed. Subsequently, efforts to improve the properties of the ionogel electrolytes, including the ionic conductivity, mechanical properties, and lithium-ion transfer number, are summarized. Besides, the applications of ionogel electrolytes in high-voltage lithium-ion batteries and lithium metal batteries as well as the batteries under extreme environments are outlined. Finally, the perspectives on studying and improving the performances of ionogel electrolytes for advanced lithium-ion batteries are provided.

Interface Engineering to Boost Thermal Safety of Microsized Silicon Anodes in Lithium-Ion Batteries.

Battery safety is vital to the application of lithium-ion batteries (LIBs), especially for high energy density cells applied in electric vehicles. As an anode material with high theoretical capacity and natural abundance, Si has received extensive attention for LIBs. However, it suffers from severe electrode pulverization during cycling due to large volume changes and an unstable solid electrolyte interphase (SEI), resulting in accelerated capacity fading and even safety hazards. Therefore, safe and long-term cycling of Si-based anodes, especially under high-temperature cycling, is highly challenging for state-of-the-art high-energy LIBs. The thermal behavior of SEI is crucial for a high safety battery as the decomposition of SEI is the first step in thermal runaway. Here, highly reversible and thermotolerant microsized Si anodes for safe LIBs are demonstrated. Comprehensive electrochemical/mechanical/thermochemical behaviors of the SEI are systematically investigated. The rational design of robust SEI endows the Si-based cells with long-term durability at elevated temperatures and superior thermal safety. This work paves the way for designing industrial-scale, low-cost, microsized Si anodes with applications in next-generation LIBs with high energy densities and high safety.

Ionogel-Based Membranes for Safe Lithium/Sodium Batteries.

Alkali (lithium, sodium)-based second batteries are considered one of the brightest candidates for energy-storage applications in order to utilize the random and intermittent renewable energy to achieve carbon neutrality. Conventional lithium/sodium batteries containing liquid organic electrolytes are vulnerable to electrolytes leakage and even combustion, which hinders their large-scale and reliable application. All-solid-state electrolytes which are considered to have better safety have been developed in recent years. However, most of them suffer from low ionic conductivity and large interfacial resistance with the electrode. Ionogel-electrolyte membranes composed of ionic liquids and solid matrices, have attracted much attention because of their nonvolatility, nonflammability, and superior chemical and electrochemical properties. This review focuses on the most recent advances of ionogel electrolytes that sprang up with the emerging demand and progress of safe lithium/sodium batteries. The ionogel-electrolyte membranes are discussed based on the framework components and preparation methods. Their structure and properties, including ionic conductivity, mechanical strength, electrochemical stabilities, and so on, are demonstrated in combination with their applications. The current challenges and insights on the future development of ionogel electrolytes for advanced safe lithium/sodium batteries are also proposed.

Precisely Tunable T-Nb2O5 Nanotubes via Atomic Layer Deposition for Fast-Charging Lithium-Ion Batteries.

The demand for fast-charging of lithium-ion batteries (LIBs) in modern electric transportation and wearable electronics is rapidly growing. However, commercially available graphite anodes still suffer from slow kinetics of lithium-ion diffusion and severe safety concerns of lithium plating when achieving the fast-charging goal. Here, it is demonstrated that the Li-ion diffusion kinetics of orthorhombic Nb2O5 nanotubes (T-Nb2O5 NTs) is enhanced by atomically precise manufacturing of nanoarchitectures. The controlled fabrication of T-Nb2O5 NTs with wall thicknesses from 24 to 43 nm is realized via atomic layer deposition (ALD) using electrospun polyacrylonitrile nanofibers as a sacrificing template. The wall thickness of T-Nb2O5 NTs can be precisely tuned by adjusting the number of ALD cycles. The relationship between the wall thicknesses and electrochemical performances is investigated in detail. The electrochemical kinetic analysis suggests that the lithium storage in T-Nb2O5 NTs is dominated by surface and intercalation pseudocapacitance. The morphology of T-Nb2O5 crystallites is found to have significant effects on the Li-ion insertion/extraction kinetics and the performance of the electrodes in LIBs. The resulting T-Nb2O5 NTs exhibit fast charge-storage kinetics and enable highly reversible insertion/extraction of Li ions without a phase change. This work may open up a new avenue for further development of intercalation-pseudocapacitive nanostructured materials for high-rate and ultrastable energy-storage devices.

Thermoregulating Separators Based on Phase-Change Materials for Safe Lithium-Ion Batteries.

Safety issues in lithium-ion batteries (LIBs) have aroused great interest owing to their wide applications, from miniaturized devices to large-scale storage plants. Separators are a vital component to ensure the safety of LIBs; they prevent direct electric contact between the cathode and anode while allowing ion transport. In this study, the first design is reported for a thermoregulating separator that responds to heat stimuli. The separator with a phase-change material (PCM) of paraffin wax encapsulated in hollow polyacrylonitrile nanofibers renders a wide range of enthalpy (0-135.3 J g-1 ), capable of alleviating the internal temperature rise of LIBs in a timely manner. Under abuse conditions, the generated heat in batteries stimulates the melting of the encapsulated PCM, which absorbs large amounts of heat without creating a significant rise in temperature. Experimental simulation of the inner short-circuit in prototype pouch cells through nail penetration demonstrates that the PCM-based separator can effectively suppress the temperature rise due to cell failure. Meanwhile, a cell penetrated by a nail promptly cools down to room temperature within 35 s, benefiting from the latent heat-storage of the unique PCM separator. The present design of separators featuring latent heat-storage provides effective strategies for overheat protection and enhanced safety of LIBs.

Architectural Engineering Achieves High-Performance Alloying Anodes for Lithium and Sodium Ion Batteries.

Tremendous efforts have been dedicated to the development of high-performance electrochemical energy storage devices. The development of lithium- and sodium-ion batteries (LIBs and SIBs) with high energy densities is urgently needed to meet the growing demands for portable electronic devices, electric vehicles, and large-scale smart grids. Anode materials with high theoretical capacities that are based on alloying storage mechanisms are at the forefront of research geared towards high-energy-density LIBs or SIBs. However, they often suffer from severe pulverization and rapid capacity decay due to their huge volume change upon cycling. So far, a wide variety of advanced materials and electrode structures are developed to improve the long-term cyclability of alloying-type materials. This review provides fundamentals of anti-pulverization and cutting-edge concepts that aim to achieve high-performance alloying anodes for LIBs/SIBs from the viewpoint of architectural engineering. The recent progress on the effective strategies of nanostructuring, incorporation of carbon, intermetallics design, and binder engineering is systematically summarized. After that, the relationship between architectural design and electrochemical performance as well as the related charge-storage mechanisms is discussed. Finally, challenges and perspectives of alloying-type anode materials for further development in LIB/SIB applications are proposed.

Top-Down Synthesis of Silicon/Carbon Composite Anode Materials for Lithium-Ion Batteries: Mechanical Milling and Etching.

Lithium-ion batteries (LIBs) providing high energy and power densities as well as long cycle life are in high demand for various applications. Benefitting from its high theoretical specific charge capacity of ≈4200 mAh g-1 and natural abundance, Si is nowadays considered as one of the most promising anode candidates for high-energy-density LIBs. However, its huge volume change during cycling prevents its widespread commercialization. Si/C-based electrodes, fabricated through top-down mechanical-milling technique and etching, could be particularly promising since they can adequately accommodate the Si volume expansion, buffer the mechanical stress, and ameliorate the interface/surface stability. In this Review, the current progresses in the top-down synthesis of Si/C anode materials for LIBs from inexpensive Si sources via the combination of low-cost, simple, scalable, and efficient ball-milling and etching processes are summarized. Various Si precursors as well as etching routes are highlighted in this Review. This review would be a guide for fabricating high-performance Si-based anodes.

Functional Inks for Printable Energy Storage Applications based on 2 D Materials.

Ubiquitous portable electronics and the ever-growing internet-of-things have necessitated the emergence of high-end miniaturized devices as well as associated sophisticated printing technologies. With excellent solution processability and tunable electronic properties, 2 D materials stand as a promising candidate for functional inks that are readily printable for energy-storage devices. In this Review, we outline the significance, status, and challenges that we are facing of the developments of 2 D materials-based functional inks. Then, general ink formulation and basic knowledge of printing techniques together with their rheological requirements and enabled applications in energy storage are introduced, providing guidelines for developing inks that match well with the present printing techniques. Last, but not least, we also propose the perspectives on the development of 2 D materials-based inks for energy-storage applications.

Mesopore-Induced Ultrafast Na+ -Storage in T-Nb2 O5 /Carbon Nanofiber Films toward Flexible High-Power Na-Ion Capacitors.

Hybrid Na-ion capacitors (NICs) are receiving considerable interest because they combine the merits of both batteries and supercapacitors and because of the low-cost of sodium resources. However, further large-scale deployment of NICs is impeded by the sluggish diffusion of Na+ in the anode. To achieve rapid redox kinetics, herein the controlled fabrication of mesoporous orthorhombic-Nb2 O5 (T-Nb2 O5 )/carbon nanofiber (CNF) networks is demonstrated via in situ SiO2 -etching. The as-obtained mesoporous T-Nb2 O5 (m-Nb2 O5 )/CNF membranes are mechanically flexible without using any additives, binders, or current collectors. The in situ formed mesopores can efficiently increase Na+ -storage performances of the m-Nb2 O5 /CNF electrode, such as excellent rate capability (up to 150 C) and outstanding cyclability (94% retention after 10 000 cycles at 100 C). A flexible NIC device based on the m-Nb2 O5 /CNF anode and the graphene framework (GF)/mesoporous carbon nanofiber (mCNF) cathode, is further constructed, and delivers an ultrahigh power density of 60 kW kg-1 at 55 Wh kg-1 (based on the total weight of m-Nb2 O5 /CNF and GF/mCNF). More importantly, owing to the free-standing flexible electrode configuration, the m-Nb2 O5 /CNF//GF/mCNF NIC exhibits high volumetric energy and power densities (11.2 mWh cm-3 , 5.4 W cm-3 ) based on the full device, which holds great promise in a wide variety of flexible electronics.

A high-energy sodium-ion capacitor enabled by a nitrogen/sulfur co-doped hollow carbon nanofiber anode and an activated carbon cathode.

Nonaqueous Na-ion capacitors (NICs) have been recently regarded as potential sustainable power devices due to their high specific energy/power and the abundant distribution of sodium resources on the Earth. However, the power performance of current NICs is usually restricted by the kinetics imbalance between sodium deintercalation/intercalation in the anode and surface ion adsorption/desorption in the cathode. Herein, we demonstrate superior sodium-ion storage properties of nitrogen/sulfur co-doped hierarchical hollow carbon nanofibers (N/S-HCNFs) for their application as an ideal anode material for NICs. The N/S-HCNFs are fabricated through in situ gas sulfuration of a hollow polyaniline nanofiber precursor, which is obtained with the aid of citric acid templates. Benefiting from the positive synergistic effects of both N and S co-doping in carbon and the hierarchical hollow one-dimensional structure, the sodium-storage performance of N/S-HCNFs half-cell versus Na/Na+ exhibits a high capacity (∼447 mA h g-1 at 50 mA g-1), excellent rate capability (∼185 mA h g-1 at 10 A g-1), and outstanding cycling stability (no capacity decay after 3000 cycles at 5 A g-1), which is among the best sodium-ion storage performances of carbonaceous Na-storage anodes. Furthermore, a dual-carbon NIC device is constructed with N/S-HCNFs as an anode and activated carbon (AC) as a cathode, and it has a large energy density of 116.4 W h kg-1, a high power density of 20 kW kg-1 (at 48.2 W h kg-1) and a long cycle life of 3000 cycles, which is superior to most reported AC-based NICs.

Scalable Synthesis of Fe/N-Doped Porous Carbon Nanotube Frameworks for Aqueous Zn-Air Batteries.

Aqueous Zn-air batteries are emerging to be ideal next-generation energy-storage devices with high safety and high energy/power densities. However, the rational design and fabrication of low-cost, highly efficient, and durable electrocatalysts on the cathode side remain highly desired. Herein, template-assisted, scalable Fe-implanted N-doped porous carbon nanotube networks (Fe-N-CNNs) have been synthesized based on an environmentally friendly template hydroxyapatite nanowires (HAP NWs). Thanks to the hierarchical meso/micropores, high specific surface area, and abundant active sites, the optimized Fe-N-CNNs exhibit excellent oxygen reduction activity. Furthermore, the Zn-air batteries based on the Fe-N-CNNs cathode deliver a high discharge voltage of 1.27 V at a current density of 20 mA cm-2 and a large peak power density of 202.2 mW cm-2 . More far-reaching, this HAP-based template strategy opens a new avenue toward the mass production of efficient, cost-effective electrocatalysts, and the Fe-N-CNNs with hollow interiors are expected to extend their other potential uses in energy storage, molecular sieves, adsorbents, and biomedical engineering.

In situ growth of copper rhodizonate complexes on reduced graphene oxide for high-performance organic lithium-ion batteries.

Novel copper rhodizonate (CPR) complexes are in situ grown on reduced graphene oxide (rGO) through a one-pot hydrothermal method. As anode materials for LIBs, the CPR/rGO composites show outstanding electrochemical lithium-storage performances, benefitting from both the insolubility of CPR in electrolytes and the effective assembly between CPR and rGO.

Self-Assembling Hollow Carbon Nanobeads into Double-Shell Microspheres as a Hierarchical Sulfur Host for Sustainable Room-Temperature Sodium-Sulfur Batteries.

We report the use of passion fruit-like double-carbon-shell porous carbon microspheres (PCMs) as the sulfur substrate in room-temperature sodium-sulfur batteries. The PCMs are covered by microsized carbon shells on the outside and consisted of carbon nanobeads with hollow structure inside, leading to a unique multidimensional scaling double-carbon-shell structure with high electronic conductivity and strengthened mechanical properties. Sulfur is filled inside the PCMs (PCMs-S) and protected by the unique double-carbon-shell, which means the subsequently generated intermediate sodium polysulfide species cannot be exposed to the electrolyte directly and well protected inside. In addition, the inner interconnected porous structure provides room for the volume expansion of sulfur during discharge processes. It is found that the PCMs-S with a 63.6% initial Coulombic efficiency contributed to the 290 mA h g-1 at the current density of 100 mA g-1 after 350 cycles. More importantly, PCMs-S exhibited good rate performance with a capacity of 113 and 56 mA h g-1 at the current densities of 1000 and 2000 mA g-1, respectively.

Recent Advances in Porous Carbon Materials for Electrochemical Energy Storage.

Climate change and the energy crisis have promoted the rapid development of electrochemical energy-storage devices. Owing to many intriguing physicochemical properties, such as excellent chemical stability, high electronic conductivity, and a large specific surface area, porous carbon materials have always been considering as a promising candidate for electrochemical energy storage. To date, a wide variety of porous carbon materials based upon molecular design, pore control, and compositional tailoring have been proposed for energy-storage applications. This focus review summarizes recent advances in the synthesis of various porous carbon materials from the view of energy storage, particularly in the past three years. Their applications in representative electrochemical energy-storage devices, such as lithium-ion batteries, supercapacitors, and lithium-ion hybrid capacitors, are discussed in this review, with a look forward to offer some inspiration and guidelines for the exploitation of advanced carbon-based energy-storage materials.

Tandem MoP nanocrystals with rich grain boundaries for efficient electrocatalytic hydrogen evolution.

Constructing surface disorder including grain boundaries, stacking faults, and dislocation arrays in nanomaterials is an important strategy to enhance the catalytic activity of nanocatalysts. Here we report the facile synthesis of crystallographically interconnected MoP nanocrystals with abundant grain boundaries. They exhibit outstanding electrocatalytic activities for hydrogen evolution.

Flexible, High-Wettability and Fire-Resistant Separators Based on Hydroxyapatite Nanowires for Advanced Lithium-Ion Batteries.

Separators play a pivotal role in the electrochemical performance and safety of lithium-ion batteries (LIBs). The commercial microporous polyolefin-based separators often suffer from inferior electrolyte wettability, low thermal stability, and severe safety concerns. Herein, a novel kind of highly flexible and porous separator based on hydroxyapatite nanowires (HAP NWs) with excellent thermal stability, fire resistance, and superior electrolyte wettability is reported. A hierarchical cross-linked network structure forms between HAP NWs and cellulose fibers (CFs) via hybridization, which endows the separator with high flexibility and robust mechanical strength. The high thermal stability of HAP NW networks enables the separator to preserve its structural integrity at temperatures as high as 700 °C, and the fire-resistant property of HAP NWs ensures high safety of the battery. In particular, benefiting from its unique composition and highly porous structure, the as-prepared HAP/CF separator exhibits near zero contact angle with the liquid electrolyte and high electrolyte uptake of 253%, indicating superior electrolyte wettability compared with the commercial polyolefin separator. The as-prepared HAP/CF separator has unique advantages of superior electrolyte wettability, mechanical robustness, high thermal stability, and fire resistance, thus, is promising as a new kind of separator for advanced LIBs with enhanced performance and high safety.

Urchin-Like Ni1/3Co2/3(CO3)1/2(OH)·0.11H2O for Ultrahigh-Rate Electrochemical Supercapacitors: Structural Evolution from Solid to Hollow.

Portable electronics and electric or hybrid electric vehicles are developing in the trend of fast charge and long electric mileage, which ask us to design a novel electrode with sufficient electronic and ionic transport channels at the same time. Herein, we fabricate a uniform hollow-urchin-like Ni1/3Co2/3(CO3)1/2(OH)·0.11H2O electrode material through an easy self-generated and resacrificial template method. The one-dimensional chain-like crystal structure unit containing the metallic bonding and the intercalated OH- and H2O endow this electrode material with abundant electronic and ionic transport channels. The hollow-urchin-like structure built by nanorods contributes to the large electrode-electrolyte contact area ensuring the supply of ions at high current. CNTs are employed to transport electrons between electrode material and current collector. The as-assembled NC-CNT-2//AC supercapacitor device exhibits a high specific capacitance of 108.3 F g-1 at 20 A g-1, a capacitance retention ratio of 96.2% from 0.2 to 20 A g-1, and long cycle life. Comprehensive investigations unambiguously highlight that the unique hollow-urchin-like Ni1/3Co2/3(CO3)1/2(OH)·0.11H2O electrode material would be the right candidate for advanced next-generation supercapacitors.

Mass Production and Pore Size Control of Holey Carbon Microcages.

Architectural control of porous solids, such as porous carbon cages, has received considerable attention for versatile applications because of their ability to interact with liquids and gases not only at the surface, but throughout the bulk. Herein we report a scalable, facile spray-pyrolysis route to synthesize holey carbon microcages with mosquito-net-like shells. Using the surfaces of water droplets as the growth templates, styrene-butadiene rubber macromolecules are controllably cross-linked, and size-controllable holes on the carbon shells are generated. The as-formed carbon microcages encapsulating Si nanoparticles exhibit enhanced lithium-storage performances for lithium-ion batteries. The scalable, inexpensive synthesis of porous carbon microcages with controlled porosity and the demonstration of outstanding electrochemical properties are expected to extend their uses in energy storage, molecular sieves, catalysis, adsorbents, water/air filters, and biomedical engineering.