Microcapsule Modification Strategy Empowering Separator Multifunctionality to Enhance Safety of Lithium-Metal Batteries.

The uncontrollable growth of lithium dendrites and the flammability of electrolytes are the direct impediments to the commercial application of high-energy-density lithium metal batteries (LMBs). Herein, this study presents a novel approach that combines microencapsulation and electrospinning technologies to develop a multifunctional composite separator (P@AS) for improving the electrochemical performance and safety performance of LMBs. The P@AS separator forms a dense charcoal layer through the condensed-phase flame retardant mechanism causing the internal separator to suffocate from lack of oxygen. Furthermore, it incorporates a triple strategy promoting the uniform flow of lithium ions, facilitating the formation of a highly ion-conducting solid electrolyte interface (SEI), and encouraging flattened lithium deposition with active SiO2 seed points, considerably suppressing lithium dendrites growth. The high Coulombic efficiency of 95.27% is achieved in Li-Cu cells with additive-free carbonate electrolyte. Additionally, stable cycling performance is also maintained with a capacity retention rate of 93.56% after 300 cycles in LFP//Li cells. Importantly, utilizing P@AS separator delays the ignition of pouch batteries under continuous external heating by 138 s, causing a remarkable reduction in peak heat release rate and total heat release by 23.85% and 27.61%, respectively, substantially improving the fire safety of LMBs.

Flame-Retardant ADP/PEO Solid Polymer Electrolyte for Dendrite-Free and Long-Life Lithium Battery by Generating Al, P-rich SEI Layer.

The poly(ethylene oxide) solid polymer electrolyte (PEO SPE) has recently received much attention, however, the organic components in the SPE are still flammable. In this paper, we find that the high efficiency halogen-free aluminum (Al) diethyl hypophosphite flame retardant (ADP) is effective in reducing the flammability of PEO SPE. The SEI layer containing Al and phosphorus (P) inhibits the growth of lithium dendrite and enhances the cycle life of the battery. The capacity of a LiFePO4/SPE/Li battery containing ADP is still 123.2 mAh g-1 at 1.0 C and the Coulombic efficiency is as high as 99.95% after 1000 cycles (60 °C). At the same time, Al, P-rich SEI can inhibit the growth of lithium dendrite and the cycle stability of the battery is further enhanced.

Migration of Mn cations in delithiated lithium manganese oxides.

Li2MnO3 is an integrated component in lithium-manganese-rich nickel manganese cobalt oxides, and the conversion of Li2MnO3 to a spinel-like structure after electrochemical activation has been associated with the continuous potential decay of the material. Delithiated Li2MnO3 and delithiated LiMn2O4 were used as model materials to investigate the mechanism of forming the spinel-like structure. An in situ high-energy X-ray diffraction technique was used to trace the structural change of materials at elevated temperatures, a procedure to mimic the structural transformation during the normal cycling of batteries. It was also found that the migration of Mn atoms from the octahedral sites to tetrahedral sites is the key step for phase transformation from a monoclinic structure to a spinel structure.

Noncombustible gel polymer electrolyte inspired by bio-radicalchemistry for high voltage and high safety Ni-rich lithium batteries.

For high energy density lithium-ion batteries (LIBs) with nickel-rich ternary cathodes, the chemical degradation of electrolytes caused by free radical reactions and the hazards of thermal runaway have always been significant challenges. Inspired by the free radical scavenging of living organisms and multiphase synergistic flame retardant mechanism, we innovatively designed and prepared a multifunctional flame retardant HCCP-TMP that combines flame retardancy and free radical scavenging by combining hindered amine and cyclophosphazene. Only 1 wt% HCCP-TMP can make the polyacrylate-based gel polymer electrolyte (GPE) incombustible. Moreover, the equipped NCM811//Graphite pouch cells don't exhibit combustion behavior after thermal runaway and can resist mechanical abuse. Based on the above noncombustible GPE, the NCM811//Li battery exhibits capacity retention rate of 82.2 % after 100 cycles at a current density of 2 C and in the voltage range of 3.0-4.7 V, exhibiting excellent cyclability under high voltage. This simple molecular design simultaneously improves the fire safety and high voltage stability, demonstrating enormous application potential in the field of advanced LIBs with high safety and high energy density.

Polyacrylonitrile@metal organic frameworks composite-derived heteroatoms doped carbon@encapsulated cobalt sulfide as superb sodium ion batteries anode.

Considering the finite resources of nonrenewable fossil fuels and urgent demands of modern society, sodium ion batteries (SIBs) featuring low cost, considerable natural supply and environmental friendless, show huge prospects in energy storage field, especially in constructing massive energy storage networks. Here, we propose a facile polyacrylonitrile@metal organic frameworks composite-derived sulfuration method, for acquiring heteroatoms doped carbon@encapsulated CoS2 nanoparticles (NSPCFS@CoS2) as SIBs anode. This electrode shows long and steady cycling process at 1 A g-1. After running 2095 cycles, it maintains a capacity of 546.3 mA h g-1. An exceedingly low capacity fading ratio of 0.013% per cycle can be acquired. Also, it gives high discharge capacities of 540.7 and 493.6 mA h g-1, even at 4 and 8 A g-1, separately. In addition, NSPCFS@CoS2 possesses a comparative or even better rate capability than other CoS2 based materials and other types of metal sulfides. Overall, this electrode exhibits superior cycling and rate performances. Additionally, its Na+ reaction kinetics and storage mechanism are deeply investigated.

Controllable magnetic field aligned sepiolite nanowires for high ionic conductivity and high safety PEO solid polymer electrolytes.

Poly (ethylene oxide) (PEO) polymer electrolyte, attracts great attention owing to its excellent flexibility, good processability and high safety compared with liquid electrolytes. However, its low ionic conductivity and weak ability to suppress the lithium dendrite severely restrict the further progress of PEO. Herein, we prepare a high ionic conductivity solid polymer electrolyte for all-solid-state lithium batteries by mixing PEO and magnetically aligned functionalized sepiolite (KFSEP) nanowires. The ionic conductivity of PEO/LiTFSI/10%⊥KFSEP solid polymer electrolyte is 2.0 × 10-5 S cm-1 at 20 °C (The ionic conductivity of PEO/LiTFSI solid polymer electrolyte is 4.0 × 10-7 S cm-1 at 20 °C). The experiments and simulation analysis indicate that the aligned nanowires provide a fast-moving channel for lithium ions. The capacity of Li/PEO/LiTFSI/10%⊥KFSEP/LFP cell is 130 mAh g-1 at 1.0 C under 60 °C after 450cycles. Furthermore, Li/PEO/LiTFSI/10%⊥KFSEP/LFP cell shows 150 mAh g-1 at 0.2 C under 25 °C. The Li/PEO/LiTFSI/10%⊥KFSEP/Li cell can work normally more than 600 h, indicating the high stability and lithium dendrite suppressing function of PEO/LiTFSI/10%⊥KFSEP. Overall, a high performance solid polymer electrolyte with higher safety is constructed by incorporating magnetically aligned sepiolite nanowires into PEO.

Multifunctional High-Efficiency Additive with Synergistic Anion and Cation Coordination for High-Performance LiNi0.8Co0.1Mn0.1O2 Lithium Metal Batteries.

Safety and high energy density have long restricted the large-scale practical application of lithium metal batteries because of the unbridled growth of lithium dendrites and the rapid deteriorating cycle performance of the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode. Herein, an additive of RbNO3 with multiple functions is proposed for dendrite-free NCM811 lithium metal batteries. Benefiting from the electrostatic shielding effect formed by Rb+ during the Li+ deposition process and the solvation effect of NO3- to regulate lithium deposition, a high Coulombic efficiency of 95.02% (compared with the low Coulombic efficiency of 89.37% in the blank electrolyte) is acquired in Li//Cu cells, and the uniform growth of the lithium metal deposition with a large strawberry-like morphology is achieved. Moreover, when a cathode of NCM811 matches with a lithium metal anode, an extraordinary capacity retention of 93.67% after 200 cycles with a high Coulombic efficiency of 99.7% in the electrolyte with the RbNO3 system (a capacity retention of 80.1% with a Coulombic efficiency of 98.0% for the blank electrolyte) is achieved at 1C. This work provides guidance for the development of high-efficiency additives with dual synergistic regulation effects of anions and cations for lithium metal batteries in the future.

Anisotropic, low-tortuosity and ultra-thick red P@C-Wood electrodes for sodium-ion batteries.

Red phosphorus (P) is considered to be the most suitable electrode for sodium-ion batteries due to its low cost, earth abundance and high theoretical capacity. Numerous studies have focused on improving the low conductivity and the extremely large volume change of red P during the cycling process. However, these strategies heavily decrease the P mass loading in the electrode. Herein, inspired by natural wood, we successfully develop an ultra-thick bulk red Phosphorus@Carbon-Wood (red P@C-Wood) electrode via the vaporization-condensation process. The sodium-ion batteries assembled with the fabricated red P@C-Wood electrode provide a high areal capacity of 18 mA h cm-2 (≈5 times those of other reported electrodes) and the P mass loading of up to 8.4 mg cm-2 (≥2 times those of other reported electrodes). The combination of red phosphorus and carbonized wood provides a new strategy for people to improve the areal energy density of lithium and sodium batteries.

Fabrication of an anode composed of a N, S co-doped carbon nanotube hollow architecture with CoS2 confined within: toward Li and Na storage.

Over the years, transition metal chalcogenides (TMCs) have attracted ample attention from researchers on account of their high theoretical capacity, through which they show great potential for use in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Nevertheless, there are some serious obstacles (particle pulverization and large volume change) still in the way to achieving satisfactory cycling performance and rate property. Here, we report the preparation of a N, S co-doped carbon nanotube hollow architecture confining CoS2 (CoS2/NSCNHF) derived from bimetal-organic-frameworks. The rationally designed structure possesses excellent Li+/Na+ storage performances. Further investigation of the Li+/Na+ storage behavior indicated the presence of a partial pseudocapacitive contribution, facilitating the fast Li+/Na+ interaction/extraction process and thus giving it superb electrochemical property. This work may represent an important step forward in the fabrication of MOF-derived hierarchical hybrids combined with a hollow structure and TMCs to help such TMCs achieve their potential in energy storage systems.

Electrochemically Exfoliated Functionalized Black Phosphorene and Its Polyurethane Acrylate Nanocomposites: Synthesis and Applications.

Owing to its mechanical performance, thermal stability, and size effects, single or few-layer black phosphorus (BP) has the potential to prepare the polymer nanocomposites as a candidate of nanoadditives, similar to graphene. The step to realize the scalable exfoliation of single or few-layer BP nanosheets is crucial to BP applications. Herein, we utilized a facile, green, and scalable electrochemical strategy for generating cobaltous phytate-functionalized BP nanosheets (BP-EC-Exf) wherein the BP crystal served as the cathode and phytic acid served as a modifier and an electrolyte simultaneously. Moreover, high-performance polyurethane acrylate/BP-EC-Exf (PUA/BP-EC) nanocomposites are easily prepared by a convenient UV-curable strategy for the first time. Significantly, the conclusion of introducing BP-EC-Exf into the PUA matrix resulted in enhancement in mechanical properties of PUA in terms of the tensile strength (increased by 59.8%) and tensile fracture strain (increased by 88.1%), in the distinct improvement in flame retardancy of PUA in terms of the decreased peak heat release rate (reduced by 44.5%) and total heat release (decreased by 34.5%), and in lower intensities of pyrolysis products including toxic CO. Moreover, it was confirmed by X-ray diffraction and Raman spectra that the air stability of PUA/BP-EC nanocomposites was maintained after exposure to environmental conditions for 4 months. The air-stable BP nanosheets, which were wrapped and embedded in the PUA matrix, can achieve the isolation and protection effect. This modified electrochemical method toward the simultaneous exfoliation and functionalization of BP nanosheets provides an efficient approach for fabricating BP-polymer-based nanocomposites.

Manganese phytate dotted polyaniline shell enwrapped carbon nanotube: Towards the reinforcements in fire safety and mechanical property of polymer.

High fire hazard of epoxy resin (EP) has been an unavoidable obstruction on its wide application. Here, a manganese phytate dotted polyaniline shell enwrapped carbon nanotube (MPCNT) is facilely constructed and employed as flame retardant for EP. By adding 4.0 wt% MPCNT, the peak heat release rate, total heat release values, peak CO yields and total CO yields are decreased by 27.2, 12.3, 44.8, and 23.3%, respectively. The decreased absorbance intensity of toxic aromatic volatiles is also observed. Then, a tripartite cooperative flame retardant mechanism (a continuous barrier network, catalytic charring function of phytate, and catalytic activity of MnP/C system) is proposed. Furthermore, the storage modulus of EP composites with 2.0 and 4.0 wt% MPCNT are increased by 23.0 and 25.8% at 40 °C, respectively. Thus, the simultaneous reinforcements in fire safety and mechanical performance of EP are successfully achieved. This work may represent a significant step forward in the facile construction of functionalized carbon materials for achieving their whole potentials in polymer-matrix composite.

Self-assembly of zinc hydroxystannate on amorphous hydrous TiO2 solid sphere for enhancing fire safety of epoxy resin.

Zinc hydroxystannate (ZHS) was fabricated on the surface of amorphous hydrous TiO2 solid spheres (AHTSS) via a layer-by-layer method for improving the fire safety of epoxy resin. AHTSS@PEI@ZHS was prepared by self-assembly of AHTSS, PEI and ZHS. The well-organized fabrication process was proved by TEM, XPS, XRD and SEM tests. TG results illustrated that the incorporation of AHTSS@PEI@ZHS show a higher residue compared with the addition of AHTSS or ZHS alone. In addition, AHTSS@PEI@ZHS filled EP composites exhibits improved flame retardancy and smoke suppression properties evaluated by cone calorimeter test. TG-IR results also indicated that the catalytic labyrinth structure of AHTSS@PEI@ZHS can effectively decrease the permeation of volatile organic compounds, thereby improving the fire safety of EP resin.

In situ loading ultra-small Cu2O nanoparticles on 2D hierarchical TiO2-graphene oxide dual-nanosheets: Towards reducing fire hazards of unsaturated polyester resin.

Fire hazards have seriously hindered the commercial application of unsaturated polyester resin (UPR), and polymer inorganic nanosheet nanocomposites hold great promise in improving their flame-retardant properties. Herein, the hierarchical structured Cu2OTiO2GO nanosheets were synthesized and characterized by XRD, Raman, TEM and XPS. Then Cu2OTiO2GO nanosheets were incorporated into UPR matrix to obtain flame-retardant UPR nanocomposite. Incorporation of 2wt% Cu2OTiO2GO nanosheets into UPR matrix resulted in an obvious reduction in PHRR and THR by 29.7 and 19.1%. TG-IR-MS results revealed that toxic pyrolysis gas such as benzene, CO and aromatic compounds greatly were decreased. In addition, RIIR spectra demonstrated the limited influence of Cu2OTiO2GO nanosheets on thermal degradation of UPR matrix, and SEM images of char residues showed that Cu2OTiO2GO nanosheets could improve their compactness. Based on the analysis of gaseous and condensed phase, a plausible flame-retardant mechanism was hypothesized to elaborate how Cu2OTiO2GO nanosheets work inside the flaming UPR nanocomposite. This innovative idea may be expanded to other polymer system and open a new door to develop polymeric nanocomposites with high performance.

Probing thermally induced decomposition of delithiated Li(1.2-x)Ni(0.15)Mn(0.55)Co(0.1)O2 by in situ high-energy X-ray diffraction.

Safety of lithium-ion batteries has been a major barrier to large-scale applications. For better understanding the failure mechanism of battery materials under thermal abuse, the decomposition of a delithiated high energy cathode material, Li1.2-xNi0.15Mn0.55Co0.1O2, in the stainless-steel high pressure capsules was investigated by in situ high energy X-ray diffraction. The data revealed that the thermally induced decomposition of the delithiated transition metal (TM) oxide was strongly influenced by the presence of electrolyte components. When there was no electrolyte, the layered structure for the delithiated TM oxide was changed to a disordered Li1-xM2O4-type spinel, which started at ca. 266 °C. The disordered Li1-xM2O4-type spinel was decomposed to a disordered M3O4-type spinel phase, which started at ca. 327 °C. In the presence of organic solvent, the layered structure was decomposed to a disordered M3O4-type spinel phase, and the onset temperature of the decomposition was ca. 216 °C. When the LiPF6 salt was also present, the onset temperature of the decomposition was changed to ca. 249 °C with the formation of MnF2 phase. The results suggest that a proper optimization of the electrolyte component, that is, the organic solvent and the lithium salt, can alter the decomposition pathway of delithiated cathodes, leading to improved safety of lithium-ion batteries.