An advanced low-cost cathode composed of graphene-coated Na_(2.4)Fe_(1.8)(SO_(4))_(3) nanograins in a 3D graphene network for ultra-stable sodium storage

Iron-based electrodes have attracted great attention for sodium storage because of the distinct cost effectiveness.However,exploring suitable iron-based electrodes with high power density and long duration remains a big challenge.Herein,a spray-drying strategy is adopted to construct graphene-coated Na_(2.4)Fe_(1.8)(SO_(4))_(3) nanograins in a 3D graphene microsphere network.The unique structural and compositional advantages endow these electrodes to exhibit outstanding electrochemical properties with remarkable rate performance and long cycle life.Mechanism analyses further explain the outstanding electrochemical properties from the structural aspect.

Self-actuating protection mechanisms for safer lithium-ion batteries

Safety issue is still a problem nowadays for the large-scale application of lithium-ion batteries(LIBs)in electric vehicles and energy storage stations.The unsafe behaviors of LIBs arise from the thermal run-away,which is intrinsically triggered by the overcharging and overheating.To improve the safety of LIBs,various protection strategies based on self-actuating reaction control mechanisms(SRCMs)have been proposed,including redox shuttle,polymerizable monomer additive,potential-sensitive separator,thermal shutdown separator,positive-temperature-coefficient electrode,thermally polymerizable addi-tive,and reversible thermal phase transition electrolyte.As build-in protection mechanisms,these meth-ods can sensitively detect either the temperature change inside battery or the potential change of the electrode,and spontaneously shut down the electrode reaction at risky conditions,thus preventing the battery from going into thermal runaway.Given their advantages in enhancing the intrinsic safety of LIBs,this paper overviews the research progresses of SRCMs after a brief introduction of thermal runaway mechanism and limitations of conventional thermal runaway mitigating measures.More importantly,the current states and issues,key challenges,and future developing trends of SRCTs are also discussed and outlined from the viewpoint of practical application,aiming at providing insights and guidance for developing more effective SRCMs for LIBs.

Understanding of the sodium storage mechanism in hard carbon anodes

Hard carbon has been regarded as the most promising anode material for sodiumion batteries(SIBs)due to its low cost,high reversible capacity,and low working potential.However,the uncertain sodium storage mechanism hinders the rational design and synthesis of high-performance hard carbon anode materials for practical SIBs.During the past decades,tremendous efforts have been put to stimulate the development of hard carbon materials.In this review,we discuss the recent progress of the study on the sodium storage mechanism of hard carbon anodes,and the effective strategies to improve their sodium storage performance have been summarized.It is anticipated that hard carbon anodes with high electrochemical properties will be inspired and fabricated for large-scale energy storage applications.

A polyethylene microsphere-coated separator with rapid thermal shutdown function for lithium-ion batteries

Thermal runaway is the main factor contributing to the unsafe behaviors of lithium-ion batteries(LIBs)in practical applications.The application of separators for the thermal shutdown has been proven as an effective approach to protecting LIBs from thermal runaway.In this work,we developed a thermal shutdown separator by coating a thin layer of low-density polyethylene microspheres(PM)onto a commercial porous polypropylene(PP)membrane and investigated the thermal response behaviors of the as-prepared PM/PP separator in LIBs.The structural and thermal analysis results revealed that the coated PM layer had a porous structure,which facilitated the occurrence of normal charge-discharge reactions at ambient temperature,although it could melt completely and fuse together within very short time periods:3 s at 110℃and 1 s at 120℃,to block off the pores of the PP substrate,thereby cutting off the ion transportation between the electrodes and interrupting the battery reaction.Consequently,the PM/PP separator exhibits very similar electrochemical performance to that of a conventional separator at ambient temperature.However,it performs a rapid thermal shutdown at an elevated temperature of^110℃,thus controlling the temperature rise and maintaining the cell in a safe status.Due to its synthetic simplicity and low cost,this separator shows promise for possible application in building safe LIBs.

Mixed polyanion cathode materials:Toward stable and high-energy sodium-ion batteries

Sodium-ion batteries(SIBs)are considered as one of the most fascinating alternatives to lithium-ion batteries for grid-scale energy storage applications because of the low cost and wide abundance of sodium resources.Among various cathode materials,mixed polyanion compounds come into the spotlight as promising electrode materials due to their superior electrochemical properties,such as high working voltage,long cycling stability,and facile reaction kinetics.In this review,we summarize the recent development in the exploration of different mixed polyanion cathode materials for SIBs.We provide a comprehensive understanding of the structure-composition-performance relationship of mixed polyanion cathode materials together with the discussion of their sodium storage mechanisms.It is anticipated that further innovative works on the material design of advanced cathode materials for batteries can be inspired.

Boosting rate and cycling performance of K-doped Na_(3)V_(2)(PO_(4))_(2)F_(3) cathode for high-energy-density sodium-ion batteries

As a promising cathode material,Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)has attracted wide attention for sodium-ion batteries(SIBs)because of its high operating voltage and high structural stability.However,the low intrinsic electronic conductivity and insufficient Na ion mobility of NVPF limit its development.Herein,K-doping NVPF is prepared through a facile ball-milling combined calcination method.The effects of K-doping on the crystal structure,kinetic properties and electrochemical performance are investigated.The results demonstrate that the Na_(2.90)K_(0.10)V_(2)(PO_(4))_(3)F_(3)(K0.10-NVPF)exhibits a high capacity(120.8 mAh g^(-1) at 0.1 C),high rate capability(66 mAh g^(-1) at 30 C)and excellent cycling performance(a capacity retention of 97.5%at 1 C over 500 cycles).Also,the occupation site of K ions in the lattice,electronic band structure and Na-ion transport kinetic property in K-doped NVPF are investigated by density functional theory(DFT)calculations,which reveals that the K-doped NVPF exhibits improved electronic and ionic conductivities,and located K^(+) ions in the lattice to contribute to high reversible capacity,rate capability and cycling stability.Therefore,the K-doped NVPF serves as a promising cathode material for high-energy and high-power SIBs.

A novel Na_(8)Fe_(5)(SO_(4))_(9)@rGO cathode material with high rate capability and ultra-long lifespan for low-cost sodium-ion batteries

Sodium-ion batteries(SIBs)are regarded as the most promising technology for large-scale energy storage systems.However,the practical application of SIBs is still hindered by the lack of applicable cathode materials.Herein,a novel phase-pure polyanionic Na_(8)Fe_(5)(SO_(4))_(9) is designed and employed as a cathode material for SIBs for the first time.The Na_(8)Fe_(5)(SO_(4))_(9) has an alluaudite-type sulfate framework and small Naþion diffusion barriers.As expected,the as-synthesized Na_(8)Fe_(5)(SO_(4))_(9)@rGO exhibits a high working potential of 3.8 V(versus Na/Naþ),a superior reversible capacity of 100.2 mAh g1 at 0.2 C,excellent rate performance(~80 mAh g1 at 10 C,~63 mAh g1 at 50 C),and an ultra-long cycling life(91.9%capacity retention after 10,000 cycles at 10 C,81%capacity retention after 20,000 cycles at 50 C).We use various techniques and computational methods to comprehensively investigate the electrochemical reaction mechanisms of Na_(8)Fe_(5)(SO_(4))_(9)@rGO.

Enabling an intrinsically safe and high-energy-density 4.5 V-class Li-ion battery with nonflammable electrolyte

Developing nonflammable electrolyte with a wide electrochemical window has become an urgent demand for high-energy-density and high-safe lithium-ion batteries(LIBs).Herein,a fluorinated nonflammable phosphate electrolyte is developed to construct a safe 4.5 V-class LIB(Si-SiC-C/0.35Li2MnO3-0.65LiNi0.5Mn0.5O2).The proposed fluorinated phosphate electrolyte,0.8 M LiPF6/tris(2,2,2-trifluoroethyl)phosphate(TFEP)+5 vol%fluoroethylene carbonate(FEC)+5 vol%vinylene carbonate(VC),is not only completely nonflammable but also exhibits excellent oxidative/reductive stability on 0.35Li2MnO30.65LiNi0.5Mn0.5O2 cathode and Si-SiC-C anode.The in situ differential electrochemical mass spectrometry and X-ray photoelectron spectroscopy proved that TFEP-based electrolyte does not decompose into gases but forms a high-quality electrode-electrolyte interface on cathode surface at high working potential.The 4.5 V-class LIBs using 0.8 M LiPF6 TFEP-based nonflammable electrolyte shed some light on potential application for high-safe and low-cost larger-scale energy storage.

High performance TiP_2O_7 nanoporous microsphere as anode material for aqueous lithium-ion batteries

This work developed a facile way to mass-produce a carbon-coated TiP_2O_7 nanoporous microsphere(TPO-NMS) as anode material for aqueous lithium-ion batteries via solid-phase synthesis combined with spray drying method. TiP_2O_7 shows great prospect as anode for aqueous rechargeable lithium-ion batteries(ALIBs) in view of its appropriate intercalation potential of-0.6 V(vs. SCE) before hydrogen evolution in aqueous electrolytes. The resulting sample presents the morphology of secondary microspheres(ca. 20 μm) aggregated by carbon-coated primary nanoparticles(100 nm), in which the primary nanoparticles with uniform carbon coating and sophisticated pore structure greatly improve its electrochemical performance. Consequently, TPONMS delivers a reversible capacity of 90 mA h/g at 0.1 A/g, and displays enhanced rate performance and good cycling stability with capacity retention of 90% after 500 cycles at 0.2 A/g. A full cell containing TPO-NMS anode and LiMn_2O_4 cathode delivers a specific energy density of 63 W h/kg calculated on the total mass of anode and cathode. It also shows good rate capacity with56% capacity maintained at 10 A/g rate(vs. 0.1 A/g), as well as long cycle life with the capacity retention of 82% after 1000 cycles at 0.5 A/g.

碳微球负载CuO纳米片用作锂离子电池的高性能负极材料

氧化铜(CuO)具有高理论容量、丰富的资源以及生态友好等特点,被认为是一种理想的锂离子电池负极材料.然而,由于CuO本身的低导电性和循环时巨大的体积膨胀,它在电池应用中的容量利用率和循环稳定性仍然存在不足.本工作中,我们通过在甲壳素衍生的碳微球的内外壁上直接原位合成CuO纳米片,构造出一种三维多孔碳@CuO复合材料.得益于碳微球的三维多孔导电框架和CuO纳米片的合理分布,CuO的容量利用率和结构稳定性在充电/放电过程中得到明显改善,所制备的电极具有优越的循环稳定性和出色的可逆容量.本工作为合理设计三维碳/过渡金属氧化物杂化体并用作电池负极材料提供了新的思路.

Boosting the sodium storage performance of Prussian blue analogues via effective etching

Prussian blue analogues(PBAs)have gained significant popularity as cathode materials for sodium-ion batteries(SIBs)due to their remarkable features such as high capacity and convenient synthesis.However,PBAs usually suffer from kinetic problems during the electrochemical reactions due to sluggish Na~+diffusion in the large crystals,resulting in low-capacity utilization and inferior rate capability.In this study,we present a facile etching method aiming at activating the sodium storage sites and accelerating the Na~+transport of Na_2NiFe(CN)_6(denoted as NaNiHCF)by precisely controlling its morphologies.A progressive corner passivation phenomenon occurred in NaNiHCF during the etching process,which led to a substantial augmentation of the specific surface area as the morphology transitioned from a standard cube to a dice shape.Notably,by controlling the etching time,the obtained NaNiHCF-3 electrode exhibited boosted electrochemical performance with high reversible capacity of 83.5mAh g~(-1)(98.2%of its theoretical capacity),superior rate capability(71.2 mAh g~(-1)at 10 C),and stable cycling life-span at different temperatures.Both experimental and computational methods reveal the remarkably reversible structural evolution process and improved Na~+diffusion coefficient.We believe that this work can serve as an indispensable reference to tailor the structure of PBAs to obtain improved electrochemical performance.

Amorphous NaVOPO_(4)as a High-Rate and Ultrastable Cathode Material for Sodium-Ion Batteries

The low cost and profusion of sodium resources make sodium-ion batteries(SIBs)a potential alternative to lithium-ion batteries for grid-scale energy storage applications.However,the use of conventional cathode materials for Na-ion intercalation/deintercalation cannot satisfy the requirements of high-powered and long lifespan performance due to multiphase transition and lattice confinement.

揭示钠离子电池正极材料Na_(6-2x)Fe_(x)(SO_(4))_(3)(1.5≤x≤2.0)的结构及电化学性质

铁基硫酸盐聚阴离子材料因其成本低廉、电化学性能优异等优点,是钠离子电池大规模应用最有前景的候选材料之一.尽管Na_(2)Fe_(2)(SO_(4))_(3),Na_(2)Fe_(1.5)(SO_(4))_(3),Na_(2.4)Fe_(1.8)(SO_(4))_(3)和Na_(2.4)Fe_(1.8)(SO_(4))_(3)等Na_(6-2x)Fe_(x)(SO_(4))_(3)(NFSO-x 1.5≤x≤2.0)材料在储钠方面取得了巨大成果,但这些NFSO-x的相和结构特性仍存在争议,难以实现具有最佳电化学性能的纯相材料.本文通过实验方法和密度泛函理论计算研究了6个具有不同x的NFSO-x样品,以分析其相和结构特性.结果表明在NFSO-x的1.6≤x≤1.7区域存在纯相,部分Na离子倾向于占据Fe位点以形成更稳定的框架.NFSO-1.7在NFSO-x样品中表现出最佳的电化学性能,具有高的放电容量(0.1 C时为104.5 mAh g^(-1),接近其理论容量105 mAh g^(-1))、出色的倍率性能(30 C时为81.5 mAh g^(-1)),并在10,000次循环中具有超长的循环稳定性,容量保持率为72.4%.本研究有助于阐明铁基硫酸盐聚阴离子材料的相和结构特征,以促进其在大规模储能中的应用.

Enhanced cycling stability of antimony anode by downsizing particle and combining carbon nanotube for high-performance sodium-ion batteries

Antimony(Sb)nanoparticles(SbNP)encapsulated in multiwalled carbon nanotubes(MWCNTs)matrix has been fabricated by a facile two-step ball milling strategy,including a sand milling process to prepare Sb nanoparticles and following high-energy ball milling to synthesize SbNP-MWCNT composite.As an anode material for sodium-ion batteries(SIBs),the SbNP-MWCNT composite with high Sb content(80%)can deliver a reversible capacity of 471.1 mA hg^(-1)at 50 mA g^(-1)with an initial coulombic efficiency of 73.5%,excellent cycling stability(94.1%capacity retention at 800 mA g^(-1))and high rate capability(210.7 mA h g^(-1)at 3200 mA g^(-1)).The excellent electrochemical performance of the SbNP-MWCNT composite results from the synergistic effect of downsizing Sb particles and combining MWCNTs.

A high-loading and cycle-stable solid-phase conversion sulfur cathode using edible fungus slag-derived microporous carbon as sulfur host

Developing a high sulfur(S)-loading cathode with high capacity utilization and long term cyclability is a key challenge for commercial implementation of Li-S battery technology.To overcome this challenge,we propose a solid-phase conversion sulfur cathode by using an edible fungus slag-derived porous carbon(CFS)as sulfur host to fabricate the S/CFS composite and meanwhile,utilizing the vinyl carbonate(VC)as co-solvent of the ether-based electrolyte to in-situ form a protective layer on the S/CFS composite surface through its nucleophilic reaction with the freshly generated lithium polysulfides(LiPSs)at the very beginning of initial discharge,thus isolating the interior sulfur from the outer electrolyte and inhibiting the further generation of soluble LiPSs.Benefitting from the ultrahigh specific surface area of>3,000 m^(2)·g^(−1),ideal pore size of<4 nm,and large pore volume of>2.0 cm^(3)·g^(−1)of the CFS host matrix,the S/CFS cathode even with a high S-loading of 80 wt.%(based on the weight of S/CFS composite)can still operate in a solid-phase conversion manner in the VC-ether co-solvent electrolyte to exhibit a high reversible capacity of 1,557 mAh·g^(−1),a high rate capability with 50%remaining capacity at 2 A·g^(−1)and a high cycling efficiency of 99.9%over 500 cycles.The results presented in this work suggest that a combined action of solid-phase conversion electrochemistry and nanoarchitectured host structure may provide a new path for the design and development of practical lithium-sulfur batteries.

Surface-engineering enhanced sodium storage performance of Na_3V_2(PO_4)_3 cathode via in-situ self-decorated conducting polymer route

The key to the development of sodium ion battery is materials with a high rate capacity and cycle stability. Conducting coating is an efficient approach to improve electrochemical performance. As a case study, the Na_3V_2(PO_4)_3@PEDOT composite was prepared through an in-situ self-decorated conducting polymer route without further calcination. The Na_3V_2(PO_4)_3 electrode with a 7%poly(3,4-ethylenedioxythiophene)(PEDOT) coating can deliver an initial reversible capacity of 100 mA h g^(-1) at 1 cycle, and 82%capacity retention over 200 cycles. The results also show that the Na_3V_2(PO_4)_3 electrode without and with a thick PEDOT coating exhibits poor electrochemical performance, indicating that an appropriate coating layer is important for improving electronic conductivity and regulating Na-ion insertion. Therefore, this work offers possibility to promote the electrochemical performance of poor-conducting materials in sodium-ion batteries using an in-situ self-decorated conducting polymer.