Approaching Ultimate Synthesis Reaction Rate of Ni-Rich Layered Cathodes for Lithium-Ion Batteries

Nickel-rich layered oxide LiNi_(x)Co_(y)MnzO_(2)(NCM,x+y+z=1)is the most promising cathode material for high-energy lithium-ion batteries.However,conventional synthesis methods are limited by the slow heating rate,sluggish reaction dynamics,high energy consumption,and long reaction time.To overcome these chal-lenges,we first employed a high-temperature shock(HTS)strategy for fast synthesis of the NCM,and the approaching ultimate reaction rate of solid phase transition is deeply investigated for the first time.In the HTS process,ultrafast average reaction rate of phase transition from Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)_(2) to Li-containing oxides is 66.7(%s^(-1)),that is,taking only 1.5 s.An ultrahigh heating rate leads to fast reaction kinetics,which induces the rapid phase transition of NCM cathodes.The HTS-synthesized nickel-rich layered oxides perform good cycling performances(94%for NCM523,94%for NCM622,and 80%for NCM811 after 200 cycles at 4.3 V).These findings might also assist to pave the way for preparing effectively Ni-rich layered oxides for lithium-ion batteries.

Texture and Se vacancy optimization induces high thermoelectric performance in Bi_(2)Se_(3) flexible thin films

Bi_(2)Se_(3)-based flexible thin film with high thermoelectric performance is promising for the waste heat recovery technology.In this work,a novel post-selenization method is employed to prepare n-type Bi_(2)Se_(3)flexible thin films with highly textured structure.The strengthened texture and Se vacancy optimization can be simultaneously achieved by optimizing the selenization temperature.The highly oriented texture leads to the increased carrier mobility and results in a high electric conductivity of~290.47 S·cm^(-1)at 623 K.Correspondingly,a high Seebeck coefficient(>110μW·K-1)is obtained due to the reduced carrier concentration,induced by optimizing vacancy engineering.Consequently,a high power factor of 3.49μW·cm^(-1)·K^(-2)at 623 K has been achieved in asprepared highly-bendable Bi_(2)Se_(3)flexible thin films selenized at 783 K.This study introduces an effective post-selenization method to tune the texture structure and vacancies of Bi_(2)Se_(3)flexible thin films,and correspondingly achieves high thermoelectric performance.

Recycle spent graphite to defect-engineered,high-power graphite anode

Graphite is a dominant anode material for lithium-ion batteries(LIBs)due to its outstanding electrochemical performance.However,slow lithium ion(Li+)kinetics of graphite anode restricts its further application.Herein,we report that high-temperature shock(HTS)can drive spent graphite(SG)into defect-rich recycled graphite(DRG)which is ideal for high-rate anode.The DRG exhibits the charging specific capacity of 323 mAh/g at a high current density of 2 C,which outperforms commercial graphite(CG,120 mAh/g).The eminent electrochemical performance of DRG can be attributed to the recovery of layered structure and partial remaining defects of SG during ultrafast heating and cooling process,which can effectively reduce total strain energy,accelerate the phase transition in thermodynamics and improve the Li+diffusion.This study provides a facile strategy to guide the re-graphitization of SG and design high performance battery electrode materials by defect engineering from the atomic level.

One-step post-treatment boosts thermoelectric properties of PEDOT:PSS flexible thin films

Developing high-performance poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)sig-nificantly widens the practical applications of flexible organic thermoelectric devices,while the water-based co-solvent dopants and/or post-treatments are still rarely studied so far.Here,we develop a one-step post-treatment to improve the power factor of PEDOT:PSS films by using a water-based solution,which is composed of co-solvent(polar solvent dimethylacetamide(DMAC)and deionized water)and organic reducing agent L-ascorbic acid(LAA).The 80 vol.%DMAC solution significantly boosts the room-temperature electrical conductivity of the films from 5 to 964 S cm^(−1),while the Seebeck coefficient can be further enhanced from 18.7 to 25μV K−1 by treating with 0.5 mol L−1 LAA,contributing to a sig-nificantly improved power factor of 55.3μW m^(−1)K^(−2).The boosted electrical conductivity is ascribed to the separated PEDOT and PSS phases triggered by the high dielectric constant and polarity of DMAC;while the improved Seebeck coefficient is attributed to the reduced oxidation degree of PEDOT from the reducing agent LAA,both confirmed by the comprehensive structural and morphological characteri-zations.Furthermore,a maximum power factor of 64.4μW m^(−1)K^(−2)can be achieved at 360 K and the observed temperature-dependent electrical transport behavior can be well explained by the Mott variable range hopping model.Besides,a flexible thermoelectric device,assembled by the as-fabricated PEDOT:PSS films,exhibits a maximum output power of∼23 nW at a temperature difference of 25 K,indicating the potential for applying to low-grade wearable electronics.

元素掺杂对钠离子电池锰基层状氧化物相变的影响

由于对可再生能源和清洁能源需求的空前增长,以及锂资源的短缺和分布不均,钠离子电池作为有竞争力的替代品越来越受到关注.钠离子层状氧化物材料,特别是锰层状氧化物材料,如P2-Na_(x)MnO_(2),P′2-Na_(x)MnO_(2),P2-Na_(0.67)Ni_(0.33)Mn_(0.67O2),O3-NaNi_(0.5)Mn_(0.5O2)等,具有结构简单、易于合成的优点,因此表现出较高的商业化生产可行性.然而,这些材料普遍面临的挑战是不可逆相变引起的不良循环性能.元素掺杂是抑制不可逆相变,改善材料性能的有效策略.本文综述了锰基层状氧化物材料中元素掺杂的研究进展,并探讨了元素掺杂对晶体结构和结构演化的影响.

Condensed point defects enhance thermoelectric performance of rare-earth Lu-doped GeTe

Heavy rare-earth element doping can effectively strengthen phonon scattering,suppress the lattice thermal conductivity,and enhance the overall thermoelectric performance of GeTe.However,the large electronegativity difference between rare-earth elements(such as La,Eu,and Gd)and Ge refrains the doping limit of rare-earth elements below 1 mol.%in GeTe.Here,compared with other rare earth elements,Lu was found to have a relatively small radius and electronegativity difference with Ge,which can induce a high doping level in GeTe.The result shows that Lu doping effectively reduces the lattice thermal conductivity from 0.77 W^(−1) m K^(−1) of GeTe to 0.35 W m^(−1) K^(−1) of Ge_(0.98)Lu_(0.02)Te at 673 K,and further induces a high zT value of 1.5 in Ge_(0.98)Lu_(0.02)Te at 673 K.Extra Sb alloying optimizes the carrier concentration from 1.02×10^(21) cm^(−3) of Ge_(0.98)Lu_(0.02)Te to 1.77×10^(20) cm^(−3) of Ge0.90Lu0.02Sb0.08Te,which results in a reasonable power factor of 33.82μW cm^(−1) K^(−2) and a low electrical thermal conductivity of 0.75 W m^(−1) K^(−1) at 673 K in Ge_(0.90)Lu_(0.02)Sb_(0.08)Te.Correspondingly,a peak zT of 1.75 at 673 K and an average zT of 0.92 within the temperature range of 303–723 K are obtained in Ge_(0.9)Lu_(0.02)Sb_(0.08)Te.This study indicates that Lu and Sb co-doping can effectively boost the thermoelectric performance of GeTe-based thermoelectric materials.

Advances in bismuth-telluride-based thermoelectric devices: Progress and challenges

By effectively converting waste heat into electricity,thermoelectric materials and devices can provide an alternative approach to tackle the energy crisis.Amongst thermoelectric materials,bismuth telluride(Bi_(2)Te_(3))and its derivatives exhibit high figure of merit ZT values in the near-room-temperature region and show great potential for application in thermoelectric devices.Considering the rapid development of Bi_(2)Te_(3)-based thermoelectric materials and their devices in the last few years,a short and systematic review is much needed.Here,we sum-marize the novel designs,properties,and applications of Bi_(2)Te_(3)-based thermoelectric devices in different contexts,including wearable,portable,implantable,and cross-disciplinary applications.The challenges and outlook for Bi_(2)Te_(3)-based thermoelectric devices are also considered.This work will guide the future development of Bi_(2)Te_(3)-based thermoelectric devices that target broader and more practical applications.

Co-free/Co-poor high-Ni cathode for high energy,stable and low-cost lithium-ion batteries

Advanced cathode materials have been considered as the key to significantly improve the energy density of lithium-ion batteries(LIBs).High-Ni layer-structured cathodes,especially with Ni atomic content above 0.9(LiN1_(x)M_(1-x)O_(2),x≥0.9),exhibit high capacity to be commercially available in electric vehicles(EVs).However,the intrinsic structure instability of high-Ni materials and the negative impacts severely restrict their further applic ation.In addition,Co has various effective efforts to stabilize the layered structure.Nevertheless,due to the high cost of Co,it is required to be replaced.Therefore,modification methods on increasing the stability of high-Ni cathode with the reduction of Co content have been widely investigated.In this review,we summarized various effective research progresses and several potential modification strategies of Cofree/Co-poor layered c athodes with Ni content over 0.9.The challenges and development opportunities of high-Ni,Cofree/Co-poor cathodes are further overviewed to meet the future commercial energy demands.

Cryo-EM for nanomaterials:Progress and perspective

Cryogenic electron microscopy(cryo-EM)has extensively boosted structural biology research since the“resolution revolution”in the year of 2013 which was soon awarded the Nobel Prize in Chemistry in 2017.The advances in camera techniques and software algorithms enabled cryoEM to routinely characterize the three-dimensional structures of biomolecules at near-atomic resolution.Biomolecules are basically sensitive to electron irradiation damage,which can be minimized at cryo-temperature.This principle has inspired material scientists to characterize electron beam-or air-sensitive materials by cryo-EM,such as the electrodes in the lithium-ion battery,metal-organic frameworks(MOFs),covalent-organic frameworks(COFs)and zeolites.In addition,the reaction systems can be fast-frozen at vitreous ice in cryoEM,which correspondingly preserves the materials at the close-to-native state.Herein,we summarized the development and applications of both the cryo-EM technique and other emerging cryo-techniques in materials science,and energy storage and conversion.Cryo-EM techniques,capable of the direct observation of sensitive materials and electrochemical reaction processes,will greatly renew our understanding of materials science and related mechanisms.

Thermoelectric coolers:Infinite potentials for finite localized microchip cooling

With the ever-growing semiconductor and microchip industries,increasing amount and categories of personal electronics have flooded into our daily life.Overheating is the key challenge limiting further performance enhancement of the high-speed microchips in electronics.Thermoelectric cooling,a solid-state active cooling method,possesses great potential for localized cooling with the advantages of noise-free,vibration-free,maintenance-free,and liquid-media-free,and can solve the challenge in microchips.By proper material engineering,such as carrier concentration,band engineering,hierarchical architecture engineering,high performance thermoelectric materials with high potential for thermoelectric cooling have been widely developed.Through further proper device design based on state-of-art thermoelectric materials,such as vertical thin film thermoelectric device design,contact interface engineering and thermoelectric and microchip integration,thermoelectric coolers show infinite potentials for finite cooling requirement of microchips.

High thermoelectric and mechanical performance in the n-type polycrystalline SnSe incorporated with multi-walled carbon nanotubes

In this study,we introduce multi-walled carbon nanotubes(MWCNTs)in Pb/I co-doped n-type polycrys-tal SnSe to simultaneously improve its thermoelectric and mechanical properties for the first time.The introduced MWCNTs act as the“bridges”to accelerate the electron carrier transport between SnSe grains,leading to significantly increased electrical conductivity from 32.6 to 45.7 S cm^(−1) at 773 K,which con-tributes to an enhanced power factor of∼5.0μW cm^(−1) K^(−2) at this temperature.Although MWCNTs possess high intrinsic thermal conductivities,these MWCNTs,acting as nanoinclusions in the SnSe matrix to form the dense interfaces between SnSe and MWCNTs,provide extra heat-carrying phonon scattering centers,leading to a slightly reduced lattice thermal conductivity of only 0.34 W m^(−1) K^(−2) at 773 K and in turn,a high ZT of∼1.0 at this temperature.Furthermore,the introduced MWCNTs can simultane-ously act as the“binders”to bond adjacent grains,significantly improving the mechanical properties of SnSe by boosting its Vickers hardness from 39.5 to 50.5.This work indicates that our facile approach can achieve high thermoelectric and mechanical properties in n-type SnSe polycrystals with a considerable potential for applying to thermoelectric devices as n-type elements.

Optimization of sodium hydroxide for securing high thermoelectric performance in polycrystalline Sn1−xSe via anisotropy and vacancy synergy

The morphology and composition are two key factors to determine the thermoelectric performance of aqueously synthesized tin selenide(SnSe)crystals;however,their controlling is still under exploring.In this study,we report a high figure-of-merit(ZT)of1.5 at 823 K in p-type polycrystalline Sn1−xSe resulted from a synergy of morphology control and vacancy optimization,realized by carefully tuning the sodium hydroxide(NaOH)concentration during solvothermal synthesis.After a comprehensive investigation on various NaOH concentrations,it was found that an optimized NaOH amount of 10 mL with a concentration of 10 mol L^−1 can simultaneously achieve a large average crystal size and a high Sn vacancy concentration of2.5%.The large microplate-like crystals lead to a considerable anisotropy in the sintered pellets,and the high Sn vacancy level contributes to an optimum hole concentration to the level of2.3×10^19 cm^−3,and in turn a high power factor of7.4μW cm^−1 K^−2 at 823 K,measured along the direction perpendicular to the sintering pressure.In addition,a low thermal conductivity of0.41 W m^−1 K^−1 is achieved by effective phonon scattering at localized crystal imperfections including lattice distortions,grain boundaries,and vacancy domains,as observed by detailed structural characterizations.Furthermore,a competitive compressive strength of52.1 MPa can be achieved along the direction of high thermoelectric performance,indicating a mechanically robust feature.This study provides a new avenue in achieving high thermoelectric performance in SnSe-based thermoelectric materials.

Synergistic band convergence and defect engineering boost thermoelectric performance of SnTe

As an eco-friendly thermoelectric material,Sn Te has attracted extensive attention.In this study,we use a stepwise strategy to enhance the thermoelectric performance of Sn Te.Firstly,Ag Cl is doped into Sn Te to realize band convergence and enlarge the band gap of Ag Cl-doped Sn Te.Ag Cl-doping also induces dense point defects,strengthens the phonon scattering,and reduces the lattice thermal conductivity.Secondly,Sb is alloyed into Ag Cl-doped Sn Te to further optimize the carrier concentration and simultaneously reduce the lattice thermal conductivity,leading to improved thermoelectric dimensionless figure of merit,ZT.Finally,(Sn_(0.81)Sb_(0.19)Te)_(0.93)(Ag Cl)_(0.07)has approached the ZT value as high as~0.87 at 773 K,which is 272%higher than that of pristine Sn Te.This study indicates that stepwise Ag Cl-doping and Sb-alloying can significantly improve thermoelectric performance of Sn Te due to synergistic band engineering,carrier concentration optimization and defect engineering.

Se-alloying reducing lattice thermal conductivity of Ge_(0.95)Bi_(0.05)Te

High lattice thermal conductivity of intrinsic GeTe limits the wide application of GeTe-based thermoelectrics.Recently,the optimization of GeTe-based thermoelectric materials has been focusing on reducing lattice thermal conductivity via strengthening phonon scattering.In this study,we systematically studied thermoelectric properties of Se-alloyed Ge_(0.95) Bi_(0.05) Te via theoretical calculations,structural characterizations,and performance evaluations.Our results indicate that Se-alloying can induce dense point defects with mass/strain-field fluctuations and correspondingly enhance point defect phonon scattering of the Ge_(0.95) Bi_(0.05) Te matrix.Se-alloying might also change chemical bonding strength to introduce resonant states in the base frequency of Ge_(0.95) Bi_(0.05) Te matrix,which can strengthen Umklapp phonon scattering.Finally,a decreased lattice thermal conductivity from∼1.02 W m^(−1) K^(−1) to∼0.65 W m^(−1) K^(−1) at 723 K is obtained in Ge_(0.95) Bi_(0.05) Te_(1-x) Se_(x) pellets with increasing the Se content from 0 to 0.3.A peak figure of merit of∼1.6 at 723 K is achieved in Ge_(0.95) Bi_(0.05) Te_(0.7) Se_(0.3) pellet,which is∼77%higher than that of pristine GeTe.This study extends the understanding on the thermoelectric performance of GeTe.