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Graphite is the most commonly used anode material for not only commercialized lithium-ion batteries (LIBs) but also the emerging potassium-ion batteries (PIBs). However, the graphite anode in PIBs using traditional dilute ester-based electrolyte systems shows obvious capacity fading, which is in contrast with the extraordinary cyclic stability in LIBs. More interestingly, the graphite in concentrated electrolytes for PIBs exhibits outstanding cyclic stability. Unfortunately, this significant difference in cycling performance has not raised concern up to now. In this work, by comparing the cyclic stability and graphitization degree of the graphite anode upon cycling, we reveal that the underlying mechanism of the capacity fading of the graphite anode in PIBs is not the larger volume expansion of graphite caused by the intercalation of potassium ions but the continual accumulation of the solid electrolyte interphase (SEI) on the surface of graphite. By X-ray photoelectron and nuclear magnetic resonance spectroscopies combined with chemical synthesis, it is concluded that the accumulation of the SEI may mainly come from the continual deposition of a kind of oligomer component, which blocks intercalation and deintercalation of potassium ions in graphite anodes. The designed SEI-cleaning experiment further verifies the above conclusion. This finding clarifies the crucial factor determining the cyclic stability of graphite and provides scientific guidance for application of the graphite anode for PIBs.

Fast-charging sodium ion batteries remain deeply challenged by the lack of suitable carbonaceous anodes that exhibit intercalation plateau with fast kinetics. Here we develop a few-layer graphitic carbon with nanoscale architecture, which enables shortened Na

Prussian blue analogues (PBAs) are promising cathode materials for monovalent- and multivalent-ion batteries due to the large frame structure. However, the effect of vacancy in lattice on the electrochemical performance has not been clearly elucidated, hindering the further development of PBAs. Here we identify two types of different functional vacancies (defined as structural vacancy and defective vacancy) in Mn-based PBAs (MnHCF) through Synchrotron-based X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation. In-situ X-ray diffraction (XRD) shows that MnHCF with structural vacancy has a slighter structural evolution than MnHCF with defective vacancy during cycles. The electrochemical results indicate that the defective vacancy in MnHCF deteriorates the cyclic performance, whereas the structural vacancy favors ion diffusion and helps to stabilize the structure. Moreover, the structure with gradient structural vacancy was successfully introduced to K-rich MnHCF, realizing a high capacity and a remarkable improvement in long-term cyclic stability for alkali metal-ion (Li+/Na+/K+) batteries.

Prussian blue (PB) is a very promising cathode for K-ion batteries but its low electronic conductivity and deficiencies in the framework aggravate electrochemical performances. Compositing with conductive reduced graphene oxide (rGO) is an effective solution to address this problem. Nevertheless, little attention was paid to the loss of oxygen-containing functional groups on the rGO substrate during the compositing process, which weakens the interaction between PB and rGO and leads to poor electrochemical performance of PB/rGO. Herein, this interaction effect associated with surface functional groups is first openly debated. Two commonly used carbon substrates, graphene oxide (GO) and rGO, are investigated. A more stable interaction between PB and GO contributes to a higher capacity retention (91.8%) than that of PB/rGO (69.7%) after 300 cycles at a current density of 5 C. Meanwhile, polyvinylpyrrolidone (PVP) is employed to repair the weak interaction between PB and rGO substrates. PB is anchored to the rGO surface through the stable covalent linking of amide groups in PVP. A superior rate capability of 72 mA h g-1 at 10 C and an improved capacity retention of 96.5% over 800 cycles at 5 C are obtained by as-prepared PB/PVP-rGO. This study provides a deeper understanding of fabricating PB/carbon composites with a robust connection.

As emerging energy storage systems, potassium-ion batteries (PIBs) are suitable for grid-scale energy storage application due to the abundant potassium resources and low cost. It is crucial to achieve fast-charging PIBs. However, as the most promising anode candidate, graphite still faces setbacks in achieving fast charging due to poor kinetic issue. Herein, modified graphite (MG) is synthesized to realize the fast potassium ion storage. Benefiting from the enlarged graphitic space combined with unique porous microstructure, MG exhibits outstanding electrochemical performance. The optimized MG anode delivers a specific capacity of 115 mAh g−1 at 4 A g−1 and excellent cycling stability of 1500 cycles at 1 A g−1. Moreover, the full cell assembled with MG anode and Prussian Blue (PB) cathode exhibits a capacity retention of 75% after 20000 cycles at the current density of 1 A g−1. The excellent electrochemical performance is further demonstrated to be associated with dominant pseudo-capacitance behavior, i.e. surface or near-surface reversible redox reactions, which are less affected by solid electrolyte interface (SEI) than intercalation reactions. Our work proposes a strategy to optimize graphitic anode materials by regulating the microstructure and may provide insight into the synthesis of high rate carbon-based anode materials for PIBs.

Rechargeable potassium (K) metal batteries (PMBs) remain deeply challenged by the lack of suitable electrolytes that are stable against both highly reactive K anodes and 4 V-class cathodes. Despite their good reductive stability with K metal, classic potassium bis(fluorosulfonyl)amide (KFSI)-based ether electrolytes are typically used only in 3 M), is reported for the first time to be used in 4 V-class PMBs. A stable N/F-rich solid electrolyte interphase (SEI) is formed, enabling dense and uniform K deposition, especially under high current density. Remarkably, the PMBs with Prussian blue cathode exhibits an unprecedented cycle life (1000 cycles, 122 days). This work provides new perspectives of electrolyte design for 4 V-class PMBs.

Potassium-based dual ion batteries have emerged as promising alternatives to the prevailing lithium-ion batteries due to the advantages in cost and sustainability. Single-anion intercalation into graphite takes place on the cathode side, but it usually delivers a low capacity with poor Coulombic efficiency in potassium-based systems. We demonstrate the performance could be significantly boosted through synergistic dual-anion intercalation of FSI− and PF6−. The presence of PF6− helps the formation of an effective cathode electrolyte interface to allow high anionic stability up to 5.5 V, while FSI− intercalation brings about superior rate capability and long-term cyclic stability. Concurrent intercalation of FSI− and PF6− is tracked by in-situ Raman spectroscopy and ex-situ XRD. It reveals the formation of stage I graphite intercalation compounds (GICs) upon charging, leading to a reversible capacity of over 100 mAh g−1 with an average potential of 4.65 V (vs. K+/K). Furthermore, the graphite-potassium cell delivers an exceptional capacity of 94 mAh g−1 at 0.3 A g−1 and shows capacity retention of 96% after 250 cycles. The strategy provides a novel avenue toward stable dual-ion battery via intercalation chemistry regulation.

Sodium and potassium metal batteries are being developed and studied enthusiastically by researchers, but the electrochemical deposition mechanism of sodium and potassium are still elusive and considered as analogs of the lithium version. In this study, it is found that the deposition of sodium and potassium are different from lithium. During deposition, cations get electrons and turn into metal deposited beneath the solid electrolyte interphase (SEI), and consequently the SEI is subject to the pressure from the metal around the deposition sites. Under the pressure, the SEI of lithium is strong enough to keep its integrity, which leads to the root growth of deposits. The lithium deposits are whiskers with the diameter of submicrometer and can be blocked by separators with the pores of dozens of nanometers. By contrast, the SEIs of sodium and potassium are weak and break into fragments under the pressure, and the subsequent deposition occur on the metal surfaces. The deposits grow into micro-scale granules and spread through the nanopores of separators, which causes the short circuit.

As a promising anode for potassium-ion batteries (PIBs), graphite has drawn great attention due to easy availability, low cost and formation of potassium-based intercalation compound. However, poor cyclic and rate performances due to severe structural degradation limit the practical application of graphite anode. Herein, a low cost mildly-expanded graphite (MEG) with adjustable interlayer lattice distance is synthesized through a wet chemical oxidation route. As anode for PIBs, the MEG exhibited stable intercalation/deintercalation plateaus, outstanding cyclic stability and rate performance. By optimizing the mass ratio between graphite and potassium permanganate oxidant, the MEG anode retaining long-range-ordered domains of graphite delivers a capacity of 88 mAh/g at 1500 mA/g and a capacity retention of 72.3% after 200 cycles at 100 mA/g. The potassium ion full cell assembled with MEGs anode exhibites high energy density and outstanding cyclic stability. Our results demonstrate a promising graphite-based anode for PIBs and provide guidance for the designing of novel carbonic electrodes for PIBs.

The all-ceramic RuO2@La0.7Ca0.3CuO3 membrane cathode contributes to an ultra-high capacity of 21 518 mA h g−1 over 110 cycles in Li–O2 batteries. A simple infiltration technique is effective for obtaining a highly active supported RuO2 catalyst, and a solvent with a high donor number should be preferentially chosen because it contributes to a much higher capacity.

We report a highly concentrated electrolyte consisting of 4 M potassium bis(fluorosulfonyl)imide (KFSI) in diethylene glycol dimethyl ether (DEGDME). This new electrolyte enables stable cycling of K metal anodes with a high CE (over 98% over 400 cycles), and excellent capacity retention (99.7% after 500 cycles) of K||potassium Prussian blue (KPB) batteries.

Potassium-ion batteries (PIBs) as an alternative to lithium-ion batteries have attracted much interest and develop rapidly. Among the cathode materials, polyanionic compounds present both high disc...

Poor oxidation stability of ether solvents at the cathode restricts the use of dilute ether electrolytes with conventional concentrations around 1 M in high-voltage lithium metal batteries. Here we develop an anion-adsorption approach to altering the ether solvent environment within the electrical double layer (EDL) at the cathode, by adding a small amount of nitrate, so that the oxidation tolerance of nitrate-containing dilute ether electrolytes is enhanced up to 4.4 V (versus Li/Li+), leading to complete compatibility with high-voltage cathodes and exhibiting superior cycling stability. Constant-potential molecular dynamics simulations reveal that ether molecules are mostly excluded from the cathode because of nitrate occupation in the inner layer of the EDL, thus suppressing ether oxidative decomposition. This work highlights that regulating the interfacial structure by adding surface adsorbates, rather than passivating cathode-electrolyte interphase or changing ion solvation, can help to enhance the oxidation stability of ether solvents. It also provides design criteria for adsorption-type additives to achieve high-voltage dilute ether electrolytes.

Nowadays, alkali metal-oxygen batteries such as Li-, Na-, and K-O2 batteries have been investigated extensively because of their ultrahigh energy density. However, the oxygen crossover of oxygen ba...

The replacement of lithium metal by lithium intercalated graphite was crucial for developing safe lithium-ion batteries. Superoxide-based potassium–oxygen batteries represent an exciting metal–oxygen battery with the highest energy efficiencies. However, using potassium metal is a more serious safety threat than lithium. Herein, we explore the possibility of graphite-intercalation anodes for potassium-ion oxygen batteries (PIOBs) with enhanced safety. This work demonstrates for the first time that establishing an artificial potassium salt-rich solid electrolyte interphase (SEI) enables a reversible graphite-intercalation anode (249.6 mA h g−1 after 600 cycles) in a potassium bis(trifluoromethanesulfonyl)imide (KTFSI)-based localized high-concentration electrolyte. Such an electrolyte is stable with the superoxide cathode. The PIOB delivers energy efficiencies above 90% at a depth of discharge (DOD) of 25% for 80 cycles. A three-electrode measurement shows that its overpotential mainly comes from the anode. The lifespan is limited to the gradual degradation of the artificial SEI caused by oxygen crossover. This work represents a step towards achieving holistic anode–electrolyte–cathode compatibility in a PIOB and its realistic evaluation under a controlled DOD.

Potassium-ion batteries (PIBs) have aroused considerable interest as large-scale energy storage candidates owing to a naturally abundant potassium resource and low cost. Since the birth of PIBs, the solid electrolyte interphase (SEI) has been a critical concern, which plays a vital role in the coulombic efficiency, cycling stability and even safety of batteries. However, the SEI of PIBs remains poorly understood. In this review, we begin with a discussion regarding the differences in the chemical composition and structure of the K-ion SEI versus the much better-known Li-ion and Na-ion SEI. Unanswered scientific questions on the nature of the K-ion SEI are clearly identified. We review findings used to understand the formation mechanism of the SEI on graphite, and the existence of the SEI in ether-based electrolytes is openly debated. The current understanding of the SEI on different types of anodes is comprehensively summarized and discussed, with an emphasis on how the enhanced stability of the SEI fundamentally affects the efficiency and reversibility of electrochemical reactions. Finally, we detail the major challenges of anodes and discuss the emerging research directions for further development of PIBs.

Potassium-ion battery (KIBs) as an economical and high energy candidate for grid-scale applications has drawn significant attention recently. Given the reversible formation of K-graphite intercalation compound, mass production and low price, the graphite is one of the most promising anode materials for KIBs. However, the issue on the fast capacity fading seriously limits the real application of graphite. The formation and stability of solid electrolyte interphase (SEI) at electrode/electrolyte interfaces during the potassiation/depotassiation or plating/striping processes is closely correlated to the above issue. Herein, by employing typical K/graphite batteries the effect of SEI on the capacity fading were systematically investigated in two electrolyte systems (i.e., ester (EC/DEC) and ether (DEGDME) based electrolytes). The decomposition of EC/DEC electrolyte led to the continuous thickening of SEI on K anode, which should be mainly responsible for the fast capacity decay of K/graphite batteries in EC/DEC electrolyte. The gradual distortion of graphite structure is the secondary cause. By comparison, the more stable DEGDME electrolyte and slight graphitic structure degradation lead to better cyclic stability. Additionally, the components of SEI on graphite anodes in full-cells are basically consistent with those in half-cells. In a word, our work provides a guidance for understanding the scientific issues on how the formation and the stability of SEI influences on the capacity decay in KIBs with graphite anodes.

The all-ceramic RuO

Potassium-ion batteries (PIBs) are considered to be potential alternatives to the conventional lithium-ion batteries (LIBs) due to the similar working mechanism and abundant potassium (K) resource. However, it still remains challenging to directly apply commercial graphite anodes for PIBs owing to the large K ions, which may impede the electrochemical intercalation of K ions into the graphite interlayer and result in a poor cyclic stability and rate capability. Reduced graphene oxide (rGO) has shown remarkable electrochemical performance as an anode material for PIBs due to the fact that rGO possesses more active sites with an enlarged interlayer distance. Understanding the microstructure of rGO is crucial for optimizing its K-ion storage capabilities. Herein, it is revealed that the K-ion storage behavior of rGO is strongly dependent on the thermal treatment temperature on account of the difference in microstructure. rGO graphitized at 2500 °C exhibits a superior long-term cyclic stability for 2500 cycles due to the expanded interlayer distance and the unique graphite-like structure in a long range, enabling it to endure the huge volume change during uninterrupted K-ion intercalation/deintercalation processes.

The aprotic lithium-oxygen (Li-O2) batteries based on carbon-based oxygen cathodes usually suffer from low round-trip efficiency. Here we adopt oxygen-enriched carbon nanotubes (CNTs) by acid etching treatment as the cathode, in which a low voltage plateau at ∼3.5 V during charge is exhibited and the initial round-trip efficiency is increased from 69.9% to 76.0%. An optimized integration of electrocatalytic property and electrical conductivity is crucial for the oxidized CNTs cathode to enhance the capacity and cycling performance. In particular, the surface oxygen groups can facilitate the electrocatalysis of O2 with the enhanced oxygen reduction reaction activity and induce defective lithium peroxide (Li2O2) formation due to their preferential adsorption of O2 on the oxidized CNTs. Compared to the high crystalline Li2O2 toroids, the defective Li2O2 with poor crystallinity could be decomposed at a lower charge potential, contributing to the enhanced round-trip efficiency of Li-O2 batteries.

Prussian blue analogues (PBAs) are promising cathode materials for potassium-ion batteries (PIBs) due to the large interstitial voids to accommodate K+ with large size. Mn-based PBA (MnHCF) shows high redox potential but considerable capacity degradation. By contrast, Fe-based PBA (FeHCF) exhibits good cyclic stability but relatively low redox potential. The different electrochemical performance is mainly due to different coordinated states, i.e., Fe-C≡N-Fe in FeHCF and Fe-C≡N-Mn in MnHCF. In this work, those two coordinated states are incorporated to construct Fe/Mn coexistent PBA (FeMnHCF), which shows not only high average discharge voltage (3.82 V vs. K+/K), but also excellent cyclic stability (the capacity can maintain 90 mAh g-1 after 600 cycles) in commonly used ester electrolyte. The results demonstrate that the coexistent coordinated structure not only improves the redox potential of N-coordinated Fe, but also increases the capacity contribution at high voltage (above 3.5 V). Furthermore, the coexistent structure can effectively inhibit the dissolution of transition metal (TM) elements and maintain structural integrity during K+ insertion/extraction, contributing to excellent cyclic stability. This work provides a promising strategy to design stable high-voltage PBA cathode materials.

Recently nonaqueous potassium-ion batteries (KIBs) have attracted tremendous attention, but a systematic study about the electrolytes remains lacking. Here, the stability of a commonly used electrolyte (KPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC)) at the anodes (e.g., graphite, solid K, and liquid Na–K alloy) was studied. Interesting results show that the linear DEC is unstable. Possibly attributed to stronger reducibility against the anodes for KIBs, the decomposition of DEC is initiated by the C(H2)–O bond breaking of the solvent molecule. This study shows that a systematic study to look for a more stable electrolyte is critically important for KIBs.

Understanding the electrochemical property of superoxides in alkali metal oxygen batteries is critical for the design of a stable oxygen battery with high capacity and long cycle performance. In this work, a KO2-decorated binder-free cathode is fabricated by a simple and efficient electrochemical strategy. KO2 nanoparticles are uniformly coated on the carbon nanotube film (CNT-f) through a controllable discharge process in the K–O2 battery, and the KO2-decorated CNT-f is innovatively introduced into the Li–O2 battery as the O2 diffusion electrode. The Li–O2 battery based on the KO2-decorated CNT-f cathode can deliver enhanced discharge capacity, reduced charge overpotential, and more stable cycle performance compared with the battery in the absence of KO2. In situ formed KO2 particles on the surface of CNT-f cathode assist to form Li2O2 nanosheets in the Li–O2 battery, which contributes to the improvement of discharge capacity and cycle life. Interestingly, the analysis of KO2-decorated CNT-f cathodes, af...

The formation of the insulated film-like discharge products (Li2O2) on the surface of the carbon cathode gradually hinders the oxygen reduction reaction (ORR) process, which usually leads to the premature death of the Li–O2 battery. In this work, by introducing the molecular sieve powder into the ether electrolyte, the Li–O2 battery exhibits a largely improved discharge capacity (63 times) compared with the one in the absence of this inorganic oxide additive. Meanwhile, XRD and SEM results qualitatively demonstrate the generation of the toroid Li2O2 as the dominated discharge products, and the chemical titration quantifies a higher yield of the Li2O2 with the presence of the molecular sieve additive. The addition of the molecular sieve controls the amount of the free water in the electrolyte, which distinguishes the effect of the molecular sieve and the free water on the discharge process. Hence, a possible mechanism has been proposed that the adsorption of the molecular sieves toward the soluble lithium ...

Amorphous silicon thin films having various thicknesses were investigated as a negative electrode material for lithium-ion batteries. Electrochemical characterization of the 20 nm thick thin silicon film revealed a very low first cycle Coulombic efficiency, which can be attributed to the silicon oxide layer formed on both the surface of the as-deposited Si thin film and the interface between the Si and the substrate. Among the investigated films, the 100 nm Si thin film demonstrated the best performance in terms of first cycle efficiency and cycle life. Observations from scanning electron microscopy demonstrated that the generation of cracks was inevitable in the cycled Si thin films, even as the thickness of the film was as little as 20 nm, which was not predicted by previous modeling work. However, the cycling performance of the 20 and 100 nm silicon thin films was not detrimentally affected by these cracks. The poor capacity retention of the 1 μm silicon thin film was attributed to the delamination.

A liquid Na-K alloy is adsorbed onto a super-aligned carbon nanotube membrane (denoted CM) at room temperature, which is driven by capillary force, fabricating a flexible CM@NaK membrane. The anode directly using the CM@NaK membrane exhibits a smooth electrode-electrolyte (liquid-liquid) interface, contributing to fast ion transport and a dendrite-free stripping/plating process.

A nitrogen (N)-doped porous carbon sheet is prepared by in situ polymerization of pyrrole on both sides of graphene oxide, following which the polypyrrole layers are then transformed to the N-doped porous carbon layers during the following carbonization, and a sandwich structure is formed. Such a sheet-like structure possesses a high specific surface area and, more importantly, guarantees the sufficient utilization of the N-doping active porous sites. The internal graphene layer acts as an excellent electron pathway, and meanwhile, the external thin and porous carbon layer helps to decrease the ion diffusion resistance during electrochemical reactions. As a result, this sandwich structure exhibits prominent catalytic activity toward the oxygen reduction reaction in alkaline media, as evidenced by a more positive onset potential, a larger diffusion-limited current, better durability and poison-tolerance than commercial Pt/C. This study shows a novel method of using graphene to template the traditional poro...

A convenient strategy is developed to prepare template-assisted, high density, porous graphene monolith (THPGM) cathodes with high densities for compact Li-O 2 batteries. Graphene oxide is used as the primary building block to construct condensed carbon electrodes by self-assembly followed by capillary drying. SiO 2 nanoparticles are incorporated onto the dense graphene monolith to function as sacrificial pore former. The bimodal pores of diameters ranging 1–6 and ∼ 40 nm created in the close-grained graphene monolith facilitate ion transport and oxygen diffusion, while providing sufficient space to accommodate the discharge products. The oxygen cathodes made from THPGM possess the advantageous features of high volumetric densities, a fully-developed porous structure and a robust architecture, resulting in unprecedented volumetric energy densities and excellent cyclic stability for Li-O 2 batteries.

Lithium-oxygen batteries (LOBs) have attracted much attention because of their extraordinarily high specific energies. They possess critical weaknesses, however, such as poor cyclic stability, low energy efficiencies, as well as serious safety issues arising from the formation of lithium dendrites. Here, we report the synthesis of a long-life Li ion O 2 battery (LIOB) consisting of an anode made from pre-lithiated aluminum (Al) foil and a Li 2 O 2 -preloaded oxygen cathode, which are both commercially available. The assembled LIOB delivers an excellent specific reversible capacity of 1000 mAh g −1 carbon for over 100 cycles at 100 mA g −1 and a maximum specific energy density of 1178 Wh kg −1 . The pre-lithiated Al foil functions as both the anode and current collector, and the stable solid electrolyte interphase layer formed on anode during pre-lithiation greatly improves the cyclic stability. In view of abundance and availability of the cathode and anode materials, the assembly strategy developed here can offer a promising route to large-scale fabrication of LIOBs for real-world applications.

In this study, a phenolic antioxidant of 2,6-di-tert-butyl-hydroxytoluene (BHT) is applied in Li-O2 batteries to simultaneously improve discharge capacity and reduce charge overpotential. BHT exhibits a redox couple at ~3.0V (vs. Li+/Li), which is extremely close to the thermodynamic potential of a Li-O2 battery (2.96V). The unique chemical and electrochemical behaviors of BHT contribute to the improvement on both oxygen reduction reaction and oxygen evolution reaction performances. These factors lead to the notable enhancement of discharge capacity (capacity increases by 72%) and the reduction of charge plateau (the plateau is 3.2V and 4.2V, respectively, with and without BHT) for Li-O2 batteries. Furthermore, in-situ X-ray diffraction results confirm that the BHT-mediated formation and decomposition of Li2O2, rather than parasitic reactions, dominate the discharge and charge processes. The results provide a new approach for exploiting appropriate soluble mediators for rechargeable Li-O2 batteries. Keywords: Li-O2 battery, Phenolic antioxidant, Bifunctional mediator, In-situ X-ray diffraction

Recently, the lithium–oxygen (Li–O2) battery has attracted much interest due to its ultrahigh theoretical energy density. However, its potential application is limited by an unstable electrolyte system, low round-trip efficiency, and poor cyclic performance. In this study, we present a new electrolyte based on N,N′-dimethylpropyleneurea (DMPU) applied for the Li–O2 battery. This electrolyte possesses high ionic conductivity and achieves a low discharge/charge voltage gap of 0.6 V, which is mainly due to the possible one-electron charge transfer mechanism. The introduction of the antioxidant butylatedhydroxytoluene (BHT) as an additive stabilizes the superoxide radical by chemical adsorption and improves the cyclic performance remarkably. Thus, this new electrolyte system may be one of the candidates for Li–O2 batteries.

A facile, low-cost precipitation method, utilizing an autogenously protective atmosphere without the assistance of an inert atmosphere, is proposed to synthesize nano-sized Prussian white K1.62Fe[Fe(CN)6]0.92·0.33H2O. The cathode delivers a high capacity of 120.9 mA h g-1 at 50 mA g-1 and an ultrahigh capacity retention of 98.2% after 100 cycles.

Hexagonal close packed Cr2O3, fabricated by an electrospinning technique combined with a heating method, is adopted for the first time as a catalyst for non-aqueous lithium–oxygen (Li–O2) batteries. The synthesized highly mesoporous Cr2O3 nanotubes (Cr2O3-MNT) with a large surface area of 53.4 m2 g−1 are confirmed by field emission scanning electron microscopy (FESEM), field emission high-resolution transmission electron microscopy (TEM) and nitrogen adsorption/desorption isotherms (BET). By using the prepared Super P (SP) (60 wt%)/Cr2O3 (30 wt%)/polyvinylidenefluoride (PVDF) (10 wt%) composite as an oxygen electrode, the Li–O2 battery shows an astonishingly enhanced capacity of 8280 mA h g−1 at a current density of 50 mA g−1. More encouragingly, when the current densities are fixed at 25, 50, 100 and 200 mA g−1 with a limited capacity of 500 mA h g−1, the charging potentials are 3.47, 3.51, 3.78 and 4.01 V, respectively, which are among the lowest charge potentials reported to date. By using a capacity-controlled method (1000 mA h g−1) at a current density of 100 mA g−1, the cell shows excellent cyclic stability up to 50 cycles. The reversible formation and dissociation of Li2O2 are verified by X-ray diffusion (XRD) and SEM, indicating that the as-prepared Cr2O3 nanotubes are a promising catalyst for Li–O2 batteries.

Lithium–oxygen batteries allow oxygen to be reduced at the battery’s cathode when a current is drawn; in present-day batteries, this results in formation of Li2O2, but it is now shown that another high energy density material, namely LiO2, with better electronic conduction can be used instead as the discharge product, if the electrode is decorated with iridium nanoparticles. Nonaqueous lithium–air batteries have a much superior theoretical gravimetric energy density compared to conventional lithium ion batteries, and thus have the potential for making long-range electric vehicles a reality. Batteries based on sodium and potassium superoxides have recently been reported, but thermodynamically unstable lithium superoxide (LiO2), with its potential high energy density, has proved more problematic. This paper demonstrates that crystalline LiO2 can be stabilized in a Li–O2 battery by using a suitable cathode material — reduced graphene oxide decorated with iridium nanoparticles. A battery based on this new lithium–oxygen chemistry was demonstrated through 40 cycles before failure, achieving high efficiency and good capacity. Batteries based on sodium superoxide and on potassium superoxide have recently been reported1,2,3. However, there have been no reports of a battery based on lithium superoxide (LiO2), despite much research4,5,6,7,8 into the lithium–oxygen (Li–O2) battery because of its potential high energy density. Several studies9,10,11,12,13,14,15,16 of Li–O2 batteries have found evidence of LiO2 being formed as one component of the discharge product along with lithium peroxide (Li2O2). In addition, theoretical calculations have indicated that some forms of LiO2 may have a long lifetime17. These studies also suggest that it might be possible to form LiO2 alone for use in a battery. However, solid LiO2 has been difficult to synthesize in pure form18 because it is thermodynamically unstable with respect to disproportionation, giving Li2O2 (refs 19, 20). Here we show that crystalline LiO2 can be stabilized in a Li–O2 battery by using a suitable graphene-based cathode. Various characterization techniques reveal no evidence for the presence of Li2O2. A novel templating growth mechanism involving the use of iridium nanoparticles on the cathode surface may be responsible for the growth of crystalline LiO2. Our results demonstrate that the LiO2 formed in the Li–O2 battery is stable enough for the battery to be repeatedly charged and discharged with a very low charge potential (about 3.2 volts). We anticipate that this discovery will lead to methods of synthesizing and stabilizing LiO2, which could open the way to high-energy-density batteries based on LiO2 as well as to other possible uses of this compound, such as oxygen storage.

The formation of the insulated film-like discharge products (Li

During the cycling of Li-O2 batteries the discharge process gives rise to dynamically evolving agglomerates composed of lithium–oxygen nanostructures; however, little is known about their composition. In this paper, we present results for a Li-O2 battery based on an activated carbon cathode that indicate interfacial effects can suppress disproportionation of a LiO2 component in the discharge product. High-intensity X-ray diffraction and transmission electron microscopy measurements are first used to show that there is a LiO2 component along with Li2O2 in the discharge product. The stability of the discharge product was then probed by investigating the dependence of the charge potential and Raman intensity of the superoxide peak with time. The results indicate that the LiO2 component can be stable for possibly up to days when an electrolyte is left on the surface of the discharged cathode. Density functional calculations on amorphous LiO2 reveal that the disproportionation process will be slower at an elec...

The safety issue caused by the dendrite growth is not only a key research problem in lithium-ion batteries but also a critical concern in alkali metal (i.e., Li, Na, and K)–oxygen batteries where a solid metal is usually used as the anode. Herein, we demonstrate the first dendrite-free K–O2 battery at ambient temperature based on a liquid Na–K alloy anode. The unique liquid–liquid connection between the liquid alloy and the electrolyte in our alloy anode-based battery provides a homogeneous and robust anode–electrolyte interface. Meanwhile, we manage to show that the Na–K alloy is only compatible in K–O2 batteries but not in Na–O2 batteries, which is mainly attributed to the stronger reducibility of potassium and relatively more favorable thermodynamic formation of KO2 over NaO2 during the discharge process. It is observed that our K–O2 battery based on a liquid alloy anode shows a long cycle life (over 620 h) and a low discharge–charge overpotential (about 0.05 V at initial cycles). Moreover, the mechani...

Raman spectroscopy is used to characterize the composition of toroids formed in an aprotic Li-O2 cell based on an activated carbon cathode. The trends in the Raman data as a function of discharge current density and charging cutoff voltage provide evidence that the toroids are made up of outer LiO2-like and inner Li2O2 regions, consistent with a disproportionation reaction occurring in the solid phase. The LiO2-like component is found to be associated with a new Raman peak identified in the carbon stretching region at ∼1505 cm(-1), which appears only when the LiO2 peak at 1123 cm(-1) is present. The new peak is assigned to distortion of the graphitic ring stretching due to coupling with the LiO2-like component based on density functional calculations. These new results on the LiO2-like component from Raman spectroscopy provide evidence that a late stage disproportionation mechanism can occur during discharge and add new understanding to the complexities of possible processes occurring in Li-O2 batteries.

Cerium substituting gadolinium in Ca2Gd8(SiO4)6O2 occupies two intrinsic sites of distinct coordination. The coexistence of an ionic bonding at a 4F site and an ionic–covalent mixed bonding at a 6H site in the same crystalline compound provides an ideal system for comparative studies of ion–ligand interactions. Experimentally, the spectroscopic properties and photoluminescence dynamics of this white-phosphor are investigated. An anomalous thermal quenching of the photoluminescence of Ce3+ at the 6H site is analyzed. Theoretically, ab initio calculations are conducted to reveal the distinctive properties of the Ce–O coordination at the two Ce3+ sites. The calculated eigenstates of Ce3+ at the 6H site suggest a weak Ce–O covalent bond formed between Ce3+ and one of the coordinated oxygen ions not bonded with Si4+. The electronic energy levels and frequencies of local vibrational modes are correlated with specific Ce–O pairs to provide a comparative understanding of the site-resolved experimental results. On...

Graphene decorated with manganese dioxide nanoparticles are prepared by electrostatic adsorption. The manganese dioxide is synthesized by a microemulsion route using the cationic surfactant hexadecyltrimethyl ammonium bromide, which dispersed in water is converted to be positively charged. The surface charge of graphene in water is negative, allowing two forms of manganese dioxide-decorated graphene to be synthesized by electrostatic adsorption: (a) free in situ synthesis and (b) layer-by-layer self-assembly. By electrochemical analysis, the specific capacitances of two materials are found to be about 40% and 250% larger than that of manganese dioxide. The improvement is because of the tighter contact between graphene and manganese dioxide, and the higher conductive and capacitive characteristics of graphene.

The lithium ion batteries using Li4Ti5O12 as the anode material are easily being inflated during charge and discharge, which, however, does not occur in the batteries using graphite as the anode material. The high reduction reactivity of electrolyte on the Li4Ti5O12 material may be the main reason. In this work, the reduction reactivities of electrolyte on the uncoated and carbon-coated Li4Ti5O12 electrodes are compared for the first time. The results show that the reduction decomposition of electrolyte does occur on the uncoated Li4Ti5O12 electrode at around 0.7 V, while it only takes place at the first cycle on the carbon-coated Li4Ti5O12 electrode. The carbon coating layers cover the catalytic active sites of Li4Ti5O12 particles and separate the Li4Ti5O12 particles from the electrolyte. A successive solid electrolyte interface (SEI) film is formed on the carbon layer during the formation process, which can prevent the further reduction decomposition of electrolyte at around 0.7 V. The impurity phases of rutile and anatase TiO2 do not influence the reduction reactivity of electrolyte. This work is not only important to understand the reduction decomposition mechanism of electrolyte on the Li4Ti5O12 electrode, but also provides an effective solution to suppress the reduction decomposition of electrolyte in the batteries.

Li4Ti5O12 anode material is synthesized using TiO2 with different crystal structure as titanium source by solid-state method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical test methods are applied to characterize the effects of TiO2 crystal structure on the structure, morphology and electrochemical performance of Li4Ti5O12. Results show that the reaction of TiO2 with Li2CO3 is an exothermic behavior. The reactivity of TiO2 with Li2CO3 gradually decreases and the particles size of Li4Ti5O12 increases with the TiO2 crystal structure changing from amorphous to rutile. The TiO2 crystal structure has a slight influence on the reversibility of Li4Ti5O12, while the specific capacities of Li4Ti5O12 at different current densities decreases obviously with the TiO2 crystal structure changing from amorphous to rutile and the sample using amorphous TiO2 as titanium sources shows highest specific capacity. The capacity retentions of all Li4Ti5O12 samples are above 97% after 50 cycles and these materials show good cycle performance. The TiO2 crystal structure has not large effects on the cycling performance of Li4Ti5O12 material.