Stable Operation Induced by Plastic Crystal Electrolyte Used in Ni-Rich NMC811 Cathodes for Li-Ion Batteries.

The LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material has been of significant consideration owing to its high energy density for Li-ion batteries. However, the poor cycling stability in a carbonate electrolyte limits its further development. In this work, we report the excellent electrochemical performance of the NMC811 cathode using a rational electrolyte based on organic ionic plastic crystal N-ethyl-N-methyl pyrrolidinium bis(fluorosulfonyl)imide C2mpyr[FSI], with the addition of (1:1 mol) LiFSI salt. This plastic crystal electrolyte (PC) is a thick viscous liquid with an ionic conductivity of 2.3 × 10-3 S cm-1 and a high Li+ transference number of 0.4 at ambient temperature. The NMC811@PC cathode delivers a discharge capacity of 188 mA h g-1 at a rate of 0.2 C with a capacity retention of 94.5% after 200 cycles, much higher than that of using a carbonate electrolyte (54.3%). Moreover, the NMC811@PC cathode also exhibits a superior high-rate capability with a discharge capacity of 111.0 mA h g-1 at the 10 C rate. The significantly improved cycle performance of the NMC811@PC cathode can be attributed to the high Li+ conductivity of the PC electrolyte, the stable Li+ conductive CEI film, and the maintaining of particle integrity during long-term cycling. The admirable electrochemical performance of the NMC811|C2mpyr[FSI]:[LiFSI] system exhibits a promising application of the plastic crystal electrolyte for high voltage layered oxide cathode materials in advanced lithium-ion batteries.

Ultrafast Charge-Discharge Capable and Long-Life Na3.9 Mn0.95 Zr0.05 V(PO4 )3 /C Cathode Material for Advanced Sodium-Ion Batteries.

Na4 MnV(PO4 )3 /C (NMVP) has been considered an attractive cathode for sodium-ion batteries with higher working voltage and lower cost than Na3 V2 (PO4 )3 /C. However, the poor intrinsic electronic conductivity and Jahn-Teller distortion caused by Mn3+ inhibit its practical application. In this work, the remarkable effects of Zr-substitution on prompting electronic and Na-ion conductivity and also structural stabilization are reported. The optimized Na3.9 Mn0.95 Zr0.05 V(PO4 )3 /C sample shows ultrafast charge-discharge capability with discharge capacities of 108.8, 103.1, 99.1, and 88.0 mAh g-1 at 0.2, 1, 20, and 50 C, respectively, which is the best result for cation substituted NMVP samples reported so far. This sample also shows excellent cycling stability with a capacity retention of 81.2% at 1 C after 500 cycles. XRD analyses confirm the introduction of Zr into the lattice structure which expands the lattice volume and facilitates the Na+ diffusion. First-principle calculation indicates that Zr modification reduces the band gap energy and leads to increased electronic conductivity. In situ XRD analyses confirm the same structure evolution mechanism of the Zr-modified sample as pristine NMVP, however the strong ZrO bond obviously stabilizes the structure framework that ensures long-term cycling stability.

Prussian blue/RGO with less coordinated water as superior cathode material for sodium-ion batteries.

A micro-cubic Prussian blue (PB) with less coordinated water is first developed by electron exchange between graphene oxide and PB. The obtained reduced graphene oxide-PB composite exhibited increased redox reactions of the Fe sites and delivered ultrahigh specific capacity of 163.3 mA h g-1 (30 mA g-1) as well as excellent cycle stability as a cathode in sodium-ion batteries.

Retraction: Prussian blue without coordinated water as a superior cathode for sodium-ion batteries.

Retraction of 'Prussian blue without coordinated water as a superior cathode for sodium-ion batteries' by Dezhi Yang et al., Chem. Commun., 2015, 51, 8181-8184, https://doi.org/10.1039/C5CC01180A.

Spray-dried assembly of 3D N,P-Co-doped graphene microspheres embedded with core-shell CoP/MoP@C nanoparticles for enhanced lithium-ion storage.

The advancement of novel synthetic approaches for micro/nanostructural manipulation of transition metal phosphide (TMP) materials with precisely controlled engineering is crucial to realize their practical use in batteries. Here, we develop a novel spray-drying strategy to construct three-dimensional (3D) N,P co-doped graphene (G-NP) microspheres embedded with core-shell CoP@C and MoP@C nanoparticles (CoP@C⊂G-NP, MoP@⊂G-NP). This intentional design shows a close correlation between the microstructural G-NP and chemistry of the core-shell CoP@C/MoP@C nanoparticle system that contributes towards their anode performance in lithium-ion batteries (LIBs). The obtained structure features a conformal porous G-NP framework prepared via the co-doping of heteroatoms (N,P) that features a 3D conductive highway that allows rapid ion and electron passage and maintains the overall structural integrity of the material. The interior carbon shell can efficiently restrain volume evolution and prevent CoP/MoP nanoparticle aggregation, providing excellent mechanical stability. As a result, the CoP@C⊂G-NP and MoP@⊂G-NP composites deliver high specific capacities of 823.6 and 602.9 mA h g-1 at a current density of 0.1 A g-1 and exhibit excellent cycling stabilities of 438 and 301 mA h g-1 after 500 and 800 cycles at 1 A g-1. The present work details a novel approach to fabricate core-shell TMPs@C⊂G-NP-based electrode materials for use in next-generation LIBs and can be expanded to other potential energy storage applications.

Improved Cycling Performance of P2-Na0.67Ni0.33Mn0.67O2 Based on Sn Substitution Combined with Polypyrrole Coating.

P2-Na0.67Ni0.33Mn0.67O2 presents high working voltage with a theoretical capacity of 173 mAh g-1. However, the lattice oxygen on the particle surface participates in the redox reactions when the material is charged over 4.22 V. The resulting oxidized oxygen aggravates the electrolyte decomposition and transition metal dissolution, which cause severe capacity decay. The commonly reported cation substitution methods enhance the cycle stability by suppressing the high voltage plateau but lead to lower average working voltage and reduced capacity. Herein, we stabilized the lattice oxygen by a small amount of Sn substitution based on the strong Sn-O bond without sacrificing the high voltage performance and further protected the particle surface by polypyrrole (PPy) coating. The obtained Na0.67Ni0.33Mn0.63Sn0.04O2@PPy (3.3 wt %) composite showed excellent cycling stability with a reversible capacity of 137.6 (10) and 120.0 mAh g-1 (100 mA g-1) with a capacity retention of 95% (10 mA g-1, 50 cycles) and 82.5% (100 mA g-1, 100 cycles), respectively. The present work indicates that slight Sn substitution combined with PPy coating could be an effective approach to achieving superior cycling stability for high-voltage layered transition metal oxides.

Enhanced Electrochemical Performance of Sodium Manganese Ferrocyanide by Na3(VOPO4)2F Coating for Sodium-Ion Batteries.

Sodium manganese ferrocyanide NaxMn[Fe(CN)6]y is an attractive cathode material for sodium-ion batteries. However, NaxMn[Fe(CN)6]y prepared by simple coprecipitation of Mn2+ and [Fe(CN)6]4- usually shows poor cycling performance, which hinders its practical application. In this work, electrochemical performance of a Na1.6Mn[Fe(CN)6]0.9 (PBM) sample prepared by the simple precipitation method was greatly improved by coating with Na3(VOPO4)2F (NVOPF) via a solution precipitation method. The as-prepared PBM@NVOPF with a coating quantity of 2.0% molar ratio showed enhanced rate capability and superior cyclic stability. The discharge capacities of PBM@NVOPF were 101.5 mA h g-1 (1 C) and 91.4 mA h g-1 (10 C), with a capacity retention of 84.3% after 500 cycles at 1 C, 20 °C. It also exhibited excellent cyclic stability at elevated temperature with an initial capacity of 109.5 mA h g-1 and a capacity retention of 78.8% after 200 cycles at 1 C, 55 °C. In comparison, uncoated PBM showed a discharge capacity of 105.7 mA h g-1 (1 C) and 76.7 mA h g-1 (10 C), with a capacity retention of only 42.0% after 500 cycles at 1 C, 20 °C. The high-temperature performance of bare PBM was very poor, and the capacity retention was only 35.7% after 40 cycles because of serious Mn/Fe dissolution which caused structural deterioration of PBM. NVOPF coating protected the PBM from suffering corrosion in the electrolyte, thus ensured the framework stability of PBM during long-term cycling and contributed to the excellent electrochemical performance.

Cobalt phosphide embedded in a graphene nanosheet network as a high-performance anode for Li-ion batteries.

Cobalt phosphide (CoP) is a potential alternative to Li-ion battery (LIB) anodes due to its high specific capacity. However, there remain challenges, including low rate capability and rapid capacity degradation, because of its structural pulverization and poor electrical conductivity. Here, we demonstrate an effective strategy to enhance CoP-based anodes by developing a CoP/graphene nanocomposite. Such a nanocomposite can be achieved by embedding nanostructured CoP in a reduced graphene oxide (rGO) nanosheet network through a versatile method including the low-temperature formation of metal oxide nanoparticles, freeze-drying, and a subsequent phosphidation process. Benefiting from its favorable nanoarchitecture, the CoP/rGO nanocomposite is found to possess enhanced conductivity, porosity and structural stability. As a result, the nanocomposite shows a high specific capacity up to 1154 mA h g-1 at a current density of 100 mA g-1 and a remarkable rate capability (840 mA h g-1 at 2 A g-1). Moreover, a high capacity of 808 mA h g-1 is achieved even after 2000 cycles. These promising features indicate that our strategy could open the door to the further applications of CoP-based anodes in LIBs.

Coaxial Carbon Nanotube Supported TiO2@MoO2@Carbon Core-Shell Anode for Ultrafast and High-Capacity Sodium Ion Storage.

The sluggish kinetic in electrode materials is one of the critical challenges in achieving high-power sodium ion storage. We report a coaxial core-shell nanostructure composed of carbon nanotube (CNT) as the core and TiO2@MoO2@C as shells for a hierarchically nanoarchitectured anode for improved electrode kinetics. The 1D tubular nanostructure can effectively reduce ion diffusion path, increase electrical conductivity, accommodate the stress due to volume change upon cycling, and provide additional interfacial active sites for enhanced charge storage and transport properties. Significantly, a synergistic effect between TiO2 and MoO2 nanostructures is investigated through ex situ solid-state nuclear magnetic resonance. The electrode exhibits a good rate capability (150 mAh g-1 at 20 A g-1) and superior cycling stability with a reversibly capacity of 175 mAh g-1 at 10 A g-1 for over 8000 cycles.

Insight into Ca-Substitution Effects on O3-Type NaNi1/3 Fe1/3 Mn1/3 O2 Cathode Materials for Sodium-Ion Batteries Application.

O3-type NaNi1/3 Fe1/3 Mn1/3 O2 (NaNFM) is well investigated as a promising cathode material for sodium-ion batteries (SIBs), but the cycling stability of NaNFM still needs to be improved by using novel electrolytes or optimizing their structure with the substitution of different elements sites. To enlarge the alkali-layer distance inside the layer structure of NaNFM may benefit Na+ diffusion. Herein, the effect of Ca-substitution is reported in Na sites on the structural and electrochemical properties of Na1-x Cax/2 NFM (x = 0, 0.05, 0.1). X-ray diffraction (XRD) patterns of the prepared Na1-x Cax/2 NFM samples show single α-NaFeO2 type phase with slightly increased alkali-layer distance as Ca content increases. The cycling stabilities of Ca-substituted samples are remarkably improved. The Na0.9 Ca0.05 Ni1/3 Fe1/3 Mn1/3 O2 (Na0.9 Ca0.05 NFM) cathode delivers a capacity of 116.3 mAh g-1 with capacity retention of 92% after 200 cycles at 1C rate. In operando XRD indicates a reversible structural evolution through an O3-P3-P3-O3 sequence of Na0.9 Ca0.05 NFM cathode during cycling. Compared to NaNMF, the Na0.9 Ca0.05 NFM cathode shows a wider voltage range in pure P3 phase state during the charge/discharge process and exhibits better structure recoverability after cycling. The superior cycling stability of Na0.9 Ca0.05 NFM makes it a promising material for practical applications in sodium-ion batteries.

Prussian blue without coordinated water as a superior cathode for sodium-ion batteries.

A micro-cubic Prussian blue (PB) without coordinated water is first developed by electron exchange between graphene oxide and PB. The obtained reduced graphene oxide-PB composite exhibited complete redox reactions of the Fe sites and delivered ultrahigh electrochemical performances as well as excellent cycling stability as a cathode in sodium-ion batteries.

Synthesis and electrochemical evolution of mesoporous LiFeSO4F0.56(OH)0.44 with high power and long cyclability.

A feasible and scalable two-step method is developed to synthesize LiFeSO4F(y)(OH)(1-y) which could deliver 92 and 80 mA h g(-1) when cycled at 1 C and 15 C, respectively. Moreover, with 80% of capacity retention after 2800 cycles at 1 C, this material should be of great interest as a contender to LiFePO4 for use in high power Li-ion batteries.

Structure optimization of Prussian blue analogue cathode materials for advanced sodium ion batteries.

A structure optimized Prussian blue analogue Na1.76Ni0.12Mn0.88[Fe(CN)6]0.98 (PBMN) is synthesized and investigated. Coexistence of inactive Ni(2+) (Fe-C≡N-Ni group) with active Mn(2+/3+) (Fe-C≡N-Mn group) balances the structural disturbances caused by the redox reactions. This cathode material exhibits particularly excellent cycle life with high capacity (118.2 mA h g(-1)).