Ionanofluid plasticized electrolyte with improved electrical and electrochemical properties for high-performance lithium polymer battery

Herein, the electrochemical characteristics of Li/LiFePO₄ battery, comprising a new class of poly (ethylene oxide) (PEO) hosted polymer electrolytes, are reported. The electrolytes were prepared using lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dopant salt and imidazolium ionic liquid-based nanofluid (ionanofluid) as the plasticizer. Morphological, thermophysical, electrical, and electrochemical properties of these newly developed electrolytes were studied. Using FT-IR spectroscopy, the interactions between dopant salt plasticizers and the host polymer, within the electrolytes, were evaluated. The optimized 30 wt% ionanofluid plasticized electrolyte exhibits a room temperature ionic conductivity of 6.33 × 10⁻³ S cm⁻¹, wide electrochemical voltage window (~4.94 V vs Li/Li⁺) along with a moderately high value of lithium-ion transference number (0.47). The values are substantially higher than that of similar wt% IL plasticized electrolyte (7.85 × 10⁻⁴ S cm⁻¹, ~4.44 V vs Li/Li⁺ and ~ 0.28, respectively). Finally, the Li/LiFePO₄ battery, comprising optimized 30 wt% ionanofluid plasticized electrolyte, delivers 156 mAh g⁻¹ discharge capacity at 0.1 C rate and able to retain its 92% value after 50 cycles. Such a superior battery performance as compared to the IL plasticized electrolyte cell (137 mAh g⁻¹ and 84% after 50 cycles at the same current rate) would endow this ionanofluid a very promising plasticizer to develop electrolytes for next-generation lithium polymer battery.     

Nitrogen/sulfur co-doped disordered porous biocarbon as high performance anode materials of lithium/sodium ion batteries

Nitrogen/sulfur co-doped disordered porous biocarbon was facilely synthesized and applied as anode materials for lithium/sodium ion batteries. Benefiting from high nitrogen (3.38 wt%) and sulfur (9.75 wt%) doping, NS_1-1 as anode materials showed a high reversible capacity of 1010.4 mA h g⁻¹ at 0.1 A g⁻¹ in lithium ion batteries. In addition, it also exhibited excellent cycling stability, which can maintain at 412 mAh g^-1 after 1000 cycles at 5 A g⁻¹. As anode materials of sodium ion batteries, NS_1-1 can still reach 745.2 mA h g⁻¹ at 100 mAg^-1 after 100 cycles. At a high current density (5 A g^-1), the reversible capacity is 272.5 mA h g⁻¹ after 1000 cycles, which exhibits excellent electrochemical performance and cycle stability. The preeminent electrochemical performance can be attributed to three effects: (1) the high level of sulfur and nitrogen; (2) the synergic effect of dual-doping heteroatoms; (3) the large quantity of edge defects and abundant micropores and mesopores, providing extra Li/Na storage regions. This disordered porous biocarbon co-doped with nitrogen/sulfur exhibits unique features, which is very suitable for anode materials of lithium/sodium ion batteries.     

Improved potassium ion storage performance of graphite by atomic layer deposition of aluminum oxide coatings

In the context of large scale and low-cost energy storage, the emerging potassium-ion batteries (PIBs) are one potential energy storage system. Graphite, a commercial anode material widely used in lithium-ion batteries (LIBs), can be directly applied to PIBs through forming the stage I graphite intercalation compound (KC₈). However, the dramatic volume expansion during the formation of KC₈ can result in poor cycling performance. In this work, one Al₂O₃ atomic layer coated on the surface of graphite via atomic layer deposition (ALD) process, aiming to construct a stable solid electrode interface and enhance the performance of graphite anode in PIBs. The electrochemical performance analysis shows that the 20 cycles Al₂O₃ deposited graphite have improved cycle stability of 223 mAh g⁻¹ at 50 mA g⁻¹ after 50 cycles compared with the raw graphite anode of 92 mAh g⁻¹.     

Temperature effect on the graphite exfoliation in propylene carbonate based electrolytes

Graphite exfoliation at a low potential has long been an issue for lithium-ion cells using a propylene carbonate (PC) based electrolyte. Two different mechanisms have been proposed in literature to explain this structural degradation. In this study, the initial lithium intercalation temperature is found to have a great impact on the extent of the graphite exfoliation. At an elevated temperature, the exfoliation can be largely suppressed and the irreversible capacity loss is reduced substantially. After the initial cycling at 50 °C, the graphite anode can be cycled in a PC-based electrolyte at room temperature without the exfoliation problem. It is also discovered that such a graphite anode gives rise to a specific capacity of over 372 mAh g⁻¹ at 50 °C and a room temperature capacity higher than that of a graphite anode with the initial lithium intercalation at room temperature. This finding sheds a new light on the exfoliation mechanism. It may lead to a simple cycling procedure that allows us to make rechargeable lithium-ion batteries with better safety and higher capacity.     

Molybdenum carbide nanocrystals modified carbon nanofibers as electrocatalyst for enhancing polysulfides redox reactions in lithium-sulfur batteries

The high performance of lithium sulfur (Li S) batteries is the focus of research in recent years. However, the low sulfur loading, shuttling effect in electrolyte, and poor cycling stability limit their applications. Herein, molybdenum carbide nanocrystals embedded carbon nanofibers (Mo₂C@CFs: MCCFs) hybrid membrane was prepared in situ on CFs membrane based on carbonthermal reduction of ammonium molybdate. The fibrous MCCFs network is used as the current collector with Li₂S₆ catholyte solution for Li S batteries, which inhibits the shuttle effect and accelerates kinetics redox reaction. In addition, Mo₂C, as electrocatalyst, promotes nucleation of Li₂S of the MCCFs substance, which can reduce polarization and increase the specific capacity. As a result, the free-standing MCCFs@Li₂S₆ electrode (sulfur loading: 4.74 mg) shows a capacity of 977 mAh g⁻¹ and maintains at 828 mAh g⁻¹ at 0.2 C over 250 cycles, and indicates excellent reversibility and cycling stability. Even with sulfur loading as high as 7.11 mg, the MCCF@Li₂S₆ electrode exhibits an extremely high capacity of 5.75 mAh. Meanwhile, the Mo₂C modified CFs can be effectively retarding the self-discharge behavior by trapping the polysulfides. Furthermore, the stability improvement of lithium anode state by effectively suppressing the shuttle effect of polysulfide, played an important role in enhancing the electrochemical performance.     

ZnSe/CoSe/NCDPH composites as anode materials for lithium ion batteries with high capacity and long cycle

In this paper, dopamine hydrochloride (DPH) is introduced to synthesize ZIF-8@ZIF-67@DPH in the preparation of ZIF-8@ZIF-67. ZnSe/CoSe/NC_DPH (N-doped carbon) composites are calcined in a high-temperature inert atmosphere with ZIF-8@ZIF-67@DPH as the precursor, selenium powder as the selenium source. ZnSe/CoSe/NC_DPH has high discharge specific capacity, good cycle stability and outstanding rate performance. The first discharge capacity of ZnSe/CoSe/NC_DPH is 1616.6 mAh g⁻¹ at the current density of 0.1 A g⁻¹, and the reversible capacity remains at 1214.2 mAh g⁻¹ after 100 cycles, the reversible capacity is 416.7 mAh g⁻¹ after 1000 cycles at 1 A g⁻¹. Therefore, ZnSe/CoSe/NC_DPH composites provide a new step for the research and synthesis of new stable, high-capacity, and safe high-performance lithium ion batteries. The bimetallic selenide composites not only have bimetallic active sites, but also can form synergistic effect between different metal phases, which can effectively reduce the capacity attenuation caused by volume expansion and reactive stress enrichment during lithium storage of metal oxide anode materials. Meanwhile, N-doped carbon can improve the conductivity and provide more active sites to store lithium, thus improving its lithium storage capacity.     

Toward high performance solid-state lithium-ion battery with a promising PEO/PPC blend solid polymer electrolyte

A promising solid polymer blend electrolyte is prepared by blending of poly(ethylene oxide) (PEO) with different content of amorphous poly(propylene carbonate) (PPC), in which the amorphous property of PPC is utilized to enhance the amorphous/free phase of solid polymer electrolyte, so as to achieve the purpose of modifying PEO-based solid polymer electrolyte. It indicates that the blending of PEO with PPC can effectively reduce the crystallization and increase the ion conductivity and electrochemical stability window of solid polymer electrolyte. When the content of PPC reaches 50%, the ionic conductivity reaches the maximum, which is 2.04 × 10⁻⁵ S cm⁻¹ and 2.82 × 10⁻⁴ S cm⁻¹ at 25°C and 60°C, respectively. The electrochemical stability window increases from 4.25 to 4.9 V and the interfacial stability of lithium metal anode is also greatly improved. The solid-state LiFePO₄//Li battery with the PEO/50%PPC blend solid polymer electrolyte has good cycling stability, which the maximum discharge specific capacity is up to 125 mAh g⁻¹ at a charge/discharge current density of 0.5 C at 60°C.     

Effects of surface lithiated TiO2 nanorods on room-temperature properties of polymer solid electrolytes

Polymer solid electrolyte with high ionic conductivity at room-temperature is most likely to be widely used in solid-state lithium batteries. In this work, the novel surface lithiated TiO₂ nanorods were firstly used as ionic conductor in polymer solid electrolyte. The surface lithiated TiO₂ nanorods-filled polypropylene carbonate polymer composite solid electrolyte (CSE) has an uniform composite structure with a thickness of about 60 μm. The ionic conductivity at room-temperature is 1.21 × 10⁻⁴ S cm⁻¹ and the electrochemical stability window is up to 4.6 V (vs Li⁺/Li). The assembled NCM622/CSE/Li solid-state battery shows a stable cycle performance with a retention capacity of 120 mAh g⁻¹ after 200 cycles at the current density of 0.3 C and a high coulomb efficiency of 99%. Compared with TiO₂ particles, this novel surface lithiated TiO₂ nanorods can provide more continuous ion transport channels and more Lewis acid-base reactive sites, provide a novel way to enhance the lithium ion transport in polymer solid electrolyte.     

Boosting the performance of poly(ethylene oxide)-based solid polymer electrolytes by blending with poly(vinylidene fluoride-co-hexafluoropropylene) for solid-state lithium-ion batteries

To seek a solid polymer electrolyte (SPE) with excellent performance, a novel poly(ethylene oxide) (PEO) based SPE is prepared by blending an appropriate amount of microcrystalline poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with PEO using a universal solution casting method. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) are utilized to analyse the samples. The crystallinity of the blend solid polymer electrolyte is significantly lower than that of the neat PEO-based SPE. The addition of the PVDF-HFP disrupts the segment structure of the PEO crystal region and increases the proportion of the amorphous region, thus boosting the migration of lithium ions. The results show that the electrochemical stability window of the blend solid polymer electrolyte reaches as high as 4.8 V. The initial discharge specific capacity of the solid-state LiFePO₄/SPE/Li battery is 131 mAh g⁻¹ at 0.5 C and 60°C, and the discharge specific capacity is still 110.5 mAh g⁻¹ after 100 cycles. On the basis of the results, the novel SPE has a widespread application prospects in solid-state lithium-ion batteries.     

Characteristics of pyrolyzed phenol-formaldehyde resin as an anode for lithium-ion batteries

Polyacenic semiconductor (PAS) is obtained by pyrolyzing phenol-formaldehyde resin (PFR). The properties of PFR heat-treated at different temperatures are investigated. The lithium intercalation capacity of PAS as a function of heat-treatment temperature (HTT) exhibits a maximum at around 700 °C. A knee appears at 700 °C, not only in the plot of atomic ratio [H]/[C] versus HTT, but also in the plot of conductivity versus HTT. For PAS with a HTT of 700 °C, the maximum in the ratio of the relative intensity of Raman spectra at 1360 cm⁻¹ corresponds to nanometer graphite, and that at 1580 cm⁻¹ to graphite. A reasonable explanation of these phenomena is the transformation of nanometer graphite to graphite.     

ZnMn2O4/milk-derived Carbon hybrids with enhanced Lithium storage capability

One of the effective ways to improve the conductivity and structural stability of binary metal oxide nanostructures is to tightly composite them with nano-carbon materials with excellent conductivity. However, the introduction of low density carbon materials also reduces the energy density of batteries. Therefore, we provides a new idea to enhance the lithium storage performance of carbon/binary transition metal oxide anode materials by multi-element co-doping carbon. ZnMn₂O₄ provides high lithium storage capacity; non-metallic heteroatoms in milk-derived carbon greatly improve the conductivity of carbon materials; metal heteroatoms in milk-derived carbon increase the density of carbon materials. Multicomponent co-doping carbon can build up the mass specific capacity, ratio performance, cyclic life and mechanical properties of binary metal oxides/porous carbon nanocomposites. As the anode materials of lithium-ion batteries, the ZnMn₂O₄/MC (milk-derived carbon) hybrids deliver a high reversible capacity of 1352 mAh g⁻¹ after 400 cycles at 0.1 A g⁻¹, and a remarkable long-term cyclability with 635 mAh g⁻¹ after 300 cycles at 1.0 A g⁻¹.     

All solid state lithium ion rechargeable batteries using NASICON structured electrolyte

Abstract

NASICON (Sodium super ionic conductor) structured Li_1·5Al_0·5Ge_1·5(PO₄)₃ (LAGP) solid electrolyte is synthesized through a solid state reaction. The total conductivity of the LAGP electrolyte is 7×10^?5 S cm^?1 with a potential window larger than 6 V. All solid state lithium batteries are fabricated using LiMn₂O₄ as a cathode, LAGP as an electrolyte and lithium metal as an anode. The LiMn₂O₄/LAGP/Li cell can deliver a capacity of about 80 mAh g^?1 in the first discharge cycle and increases gradually with charge/discharge cycles, indicating that LAGP can be used as a promising electrolyte for lithium rechargeable batteries.     

New strategy to prepare nitrogen self-doped graphene nanosheets by magnesiothermic reduction and its application in lithium ion batteries

Nitrogen self-doped graphene (N/G) nanosheets were prepared through magnesiothermic reduction of melamine. The obtained N/G features porous structure consisting of multi-layer nanosheets. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra and X-ray diffraction (XRD). As anode of lithium ion batteries (LIBs), it exhibits excellent reversible specific capacity of 1753 mAh g⁻¹ at 0.1 A g^-1 after 200 cycles. The reversible capacity can maintain at 1322 mAh g⁻¹ after 500 cycles at 2 A g⁻¹. At the same time, all results indicate remarkable cycle stability and rate performance as anode materials. Furthermore, this study demonstrates an economical, clean and facile strategy to synthesize N/G nanosheets from cheap chemicals with excellent electrochemical performance in LIBs.     

A microporous carbon derived from metal-organic frameworks for long-life lithium sulfur batteries

A polyhedral microporous carbon derived from metal-organic frameworks (ZIF-8) could present good property for sulfur loading and trapping. A melting-evaporation route was adopted to synthesize two sulfur/microporous carbon (S/MC) composites, of which sulfur content is controllable, and ether-based or ester-based electrolytes were used to evaluate the synthesized composites for the lithium sulfur batteries. According to electrochemical results, the S/MC composite with 65.2 wt% S in the ether-based electrolyte exhibited optimized performance as compared with the composite with 65.2 wt% S in the ester-based electrolyte, as well as the composite with 58.6 wt% S in the two kinds of electrolytes. For the S/MC composite with 65.2 wt% S in ether-based electrolyte, the initial discharge capacity could reach up to 1505.9 mAh g⁻¹ and the reversible capacity could be 833.3 mAh g⁻¹ after 40 cycles at 0.1 C. Furthermore, while being respectively evaluated at 0.5, 1.0, and 2.0 C, the discharge capacities could still maintain at 544, 493 and 354 mAh g⁻¹ after 300, 500, and 800 cycles, demonstrating appreciable cyclic reversibility and rate capability.     

A polyanionic anthraquinone organic cathode for pure small-molecule organic Li-ion batteries

Sodium 9,10-anthraquinone-2,6-disulfonate (Na₂AQ26DS, 130 mAh g⁻¹) with polyanionic character and two O–Na ionic bonds is used as an organic cathode for Li-ion batteries. Na₂AQ26DS exhibits highly impressive cycle stability in ether electrolytes due to its polyanionic character and the effective suppression of solvent-molecule co-intercalation. In half cells (1–3.9 V vs. Li⁺/Li) using 1 M bis(trifluoromethanesulphonyl)imide lithium salt (LiTFSI) in 1,3-dioxolane/dimethoxyethane (DOL/DME), Na₂AQ26DS delivers a highly stable specific capacity of 123 mAh g⁻¹ at 50 mA g⁻¹ for 900 cycles (6-month test) and realizes ∼69 mAh g⁻¹ for 2800 cycles at 500 mA g⁻¹. In the full cells with the reduced state (Li₄TP) of lithium terephthalate (Li₂TP) as the organic anode, the resulting Li₄TP II Na₂AQ26DS organic lithium-ion batteries (OLIBs) can display a highly stable average discharge capacity of 120 mAh g⁻¹_cathode for 100 cycles at 50 mA g⁻¹ and ∼63 mAh g⁻¹_cathode for 1200 cycles at 500 mA g⁻¹ in 0.2–3.3 V.     

A thermo-stable poly(propylene carbonate)-based composite separator for lithium-sulfur batteries under elevated temperatures

Lithium-sulfur (Li-S) batteries have a great potential for the future development of energy industry. However, the high-temperature performance of Li-S batteries is still facing great challenge due to the high flammability of the electrolyte, sulfur cathode as well as the separator. The separator modification is an effective method to improve the thermal stability of separator and the electrochemical performance of Li-S batteries under elevated temperatures. However, the reported methods of separator coating are too complicated to be applied in the industrial production. Here, a novel thermo-stable composite separator (M-Celgard-p), in which a layer of silicon dioxide-poly (propylene carbonate) based electrolyte (nano-SiO₂@PPC) with a high ionic-conductivity of 1.03 × 10⁻⁴ S cm⁻¹ is coated on the commercial Celgard-p separator, is prepared by using a simple dipping method. Compared to the Li-S battery assembled with Celgard-p separator, the M-Celgard-p separator combined with a sulfur/polyacrylonitrile (S/PAN) cathode can improve the electrochemical performance of Li-S batteries, especially their high-temperature stability. As a result, the (S/PAN)/M-Celgard-p/Li cell delivers a high specific capacity of 724.7 mAh g⁻¹ at 1.0 A g⁻¹ after 200 cycles and presents a good rate capability of 1408 mAh g⁻¹ at 1.0 A g⁻¹ and 1216 mAh g⁻¹ at 2.0 A g⁻¹. More importantly, the (S/PAN)/M-Celgard-p/Li cell can exhibit a capacity retention ratio of 69.4% after 200 cycles at 60°C. The M-Celgard-p separator with high Li-ion conductivity can not only block the “shuttle-effect” of polysulfides during cycling but also enhance the thermal stability under elevated temperatures. This work presents a simple dipping method to prepare composite separator with excellent thermal stability, which enhance the rate performance and cyclic stability of Li-S batteries under elevated temperatures. We believe this work can provide a new way to develop more reliable Li-S batteries for practical applications.     

Guided dendrite-free lithium deposition through titanium nitride additive in Li metal batteries

Metallic lithium (Li) is one of the most potential anode materials in the near future, because of its high theoretical specific capacity (3865 mAh/g), low potential (−3.045 V vs standard hydrogen electrode (SHE)) and low density (0.534 g/cm³). However, fatal dendritic Li growth is the bottleneck of the development of Li anode. In this contribution, we reported a titanium nitride (TiN) nanoparticle additive to guide Li deposition uniformly, hence dead Li and dendritic Li are effectively reduced. There are more nucleation sites on the surface of the electrode due to the stronger adsorption of Li ions on each facet of TiN, and TiN nanoparticles play the role of seeds of Li deposition. The half cells cycling in additive electrolyte exhibit an average Coulombic efficiency (CE) of 97.19% for 270 cycles on plane copper (Cu) electrode and an excellent high average CE of 99.01% for 300 cycles on three-dimensional (3D) carbon paper (CP) electrode at 1 mA/cm² and 1 mAh/cm². Li–S full cells equipped with such TiN nanoparticles additive electrolyte deliver great enhanced cycling and rate performance. This work provides a new insight to suppress Li dendrite and realizing high performance of Li metal batteries.     

Functional interface of polymer modified graphite anode

Graphite electrodes were modified by polyacrylic acid (PAA), polymethacrylic acid (PMA), and polyvinyl alcohol (PVA). Their electrochemical properties were examined in 1 mol dm⁻³ LiClO₄ ethylene carbonate:dimethyl carbonate (EC:DMC) and propylene carbonate (PC) solutions as an anode of lithium ion batteries. Generally, lithium ions hardly intercalate into graphite in the PC electrolyte due to a decomposition of the PC electrolyte at ca. 0.8 V vs. Li/Li⁺, and it results in the exfoliation of the graphene layers. However, the modified graphite electrodes with PAA, PMA, and PVA demonstrated the stable charge–discharge performance due to the reversible lithium intercalation not only in the EC:DMC but also in the PC electrolytes since the electrolyte decomposition and co-intercalation of solvent were successfully suppressed by the polymer modification. It is thought that these improvements were attributed to the interfacial function of the polymer layer on the graphite which interacted with the solvated lithium ions at the electrode interface.     

Pure ionic liquid electrolytes compatible with a graphitized carbon negative electrode in rechargeable lithium-ion batteries

Ambient temperature ionic liquids composed of bis(fluorosulfonyl)imide (FSI) as an anion and 1-ethyl-3-methylimidazolium (EMI) or N-methyl-N-propylpyrrolidinium (P-13) as a cation have the following desirable physicochemical properties, particularly for a battery electrolyte: a high ionic conductivity, low viscosity, and a low melting point. While an irreversible cationic intercalation into graphene interlayers at ca. 0.5 V versus Li/Li⁺ has been a significant and common problem with usual ionic liquids, we found that ionic liquids containing FSI with the Li cation can prevent such an irreversible reaction and provide reversible Li intercalation into graphene interlayers. Our experimental results found the reversible capacity of a graphite negative electrode, in a half-cell with EMI-FSI containing the Li cation as an electrolyte, to be a stable value of approximately 360 mAh g⁻¹ during 30 cycles at a charge/discharge rate of 0.2 C, The present paper may be the first report that a “pure” ionic liquid can provide a stable, reversible capacity for a graphitized negative electrode at an ambient temperature without any additives or solvents when an appropriate counter anion, e.g., FSI, is selected.     

Cobalt-doped layered lithium nickel oxide as a three-in-one electrode for lithium-ion and sodium-ion batteries and supercapacitor applications

Layered LiNi_0.94Co_0.06O₂ (LNCO) was prepared and explored as an energy-storage material for Li-ion (LIBs), Na-ion (SIBs) batteries as well as supercapacitor application for the first time. All the physical and morphological characterizations were studied for the sample LNCO. The result displays good thermal stability, phase purity in the crystal structure, appreciable Brunauer-Emmett-Teller (BET) surface area (5.53 m² g⁻¹) and possesses cubic morphology. The cobalt was identified in lithium nickel oxide with binding energies at 794.02, 779.04 and 784.30 eV, respectively. In the case of LIBs, LNCO exists with a minimal difference of 5 mAh g⁻¹, even when cycled from 2C to 0.1C. After 200 cycles, the specific capacity, 247 mAh g⁻¹, is obtained for the cell with retention of 97.8% (efficiency 99.8%) at 0.1C. In SIBs, at 0.1C, the discharge capacity of 182 mAh g⁻¹ was restored even when cycled after 2C. After 200 cycles, a discharge capacity of 204 mAh g⁻¹ is ensured with retention of 96.6% (efficiency of 99.4% at 0.1C). In supercapacitor, the electrode, LNCO, delivered a specific capacity of 300 F g⁻¹ at 0.5 A g⁻¹. Therefore, LNCO is highly recommended as a suitable electrode material for fulfilling the requirement of energy-storage applications.