Lithium-ion and solvent co-intercalation enhancing the energy density of fluorinated graphene cathode

Fluorinated carbons CF_xhold the highest theoretical energy density(e.g.,2180 W h kg^(-1)when x=1)among all cathode materials of lithium primary batteries.However,the low conductivity and severe polarization limit it to achieve its theory.In this study,we design a new electrolyte,namely 1 M LiBF_(4)DMSO:DOL(1:9 vol.),achieving a high energy density in Li/CF_xprimary cells.The DMSO with a small molecular size and high donor number successfully solvates Li^(+)into a defined Li^(+)-solvation structure.Such solvated Li^(+)can intercalate into the large-spacing carbon layers and achieve an improved capacity.Consequently,when discharged to 1.0 V,the CF_(1.12)cathode demonstrates a specific capacity of 1944 m A h g^(-1)with a specific energy density of 3793 W h kg^(-1).This strategy demonstrates that designing the electrolyte is powerful in improving the electrochemical performance of CF_(x) cathode.

Fluorinated soft carbon as an ultra-high energy density potassium-ion battery cathode enabled by a ternary phase K_(x)FC

Fluorinated carbons(CFx)have been widely applied as lithium primary batteries due to their ultra-high energy density.It will be a great promise if CFx can be rechargeable.In this study,we rationally tune the C-F bond strength for the alkaline intercalated CFx via importing an electronegative weaker element K instead of Li.It forms a ternary phase K_(x)FC instead of two phases(LiF+C)in lithium-ion batteries.Meanwhile,we choose a large layer distance and more defects CFx,namely fluorinated soft carbon,to accommodate K.Thus,we enable CFx rechargeable as a potassium-ion battery cathode.In detail fluorinated soft carbon CF_(1.01) presents a reversible specific capacity of 339 mA h g^(-1)(797 Wh kg^(-1))in the 2nd cycle and maintains 330 mA h g^(-1)(726 Wh kg^(-1))in the 15th cycle.This study reveals the importance of tuning chemical bond stability using different alkaline ions to endow batteries with rechargeability.This work provides good references for focusing on developing reversible electrode materials from popular primary cell configurations.

缺陷氮掺杂碳耦合Co-N5单原子位点用于高效锌-空气电池

锌-空气电池(ZAB)因其能量密度高、环境友好、成本低以及安全性高而备受关注.然而,空气电极上的氧还原反应(ORR)动力学缓慢,严重限制了ZAB的输出功率.尽管铂基催化剂展现出优异的ORR催化活性,但高昂的成本制约其大规模商业化应用.因此,迫切需要开发高效、低成本的ORR电催化剂.研究表明,具有原子分散Co-N4活性位点的Co-N-C单原子催化剂是理想的ORR非贵金属催化剂,但其仍然存在与反应关键中间体结合能较高的难题.目前的研究主要通过调控单原子配位环境与增大活性位点密度来提高Co-N-C催化剂的活性,但如何精确控制中心金属电子结构以及避免高温下金属原子的团聚仍面临巨大挑战.除了单原子活性位点外,催化剂载体的键合结构、电荷分布状态亦会影响载体本身和单原子位点的催化活性.然而,现有的研究主要聚焦于单原子位点或无金属催化剂单方面活性的提升,关于它们之间的相互作用对于催化性能影响的研究相对很少.为了进一步提高Co单原子催化剂的催化活性,本文通过简单的模板法与NH3二次处理策略制备了氮掺杂缺陷碳负载的Co-N_(5)位点单原子催化剂.电感耦合等离子体发射光谱结果表明,单原子Co的金属负载量高达2.57 wt%.此外,相比于未经过NH3二次处理的Co-Nx/HC样品,Co-N_(5)/DHC样品在电子顺磁共振谱中g=2.003处呈现出更明显的共振信号,在C 1s高分辨谱中具有更低的C-C(sp2杂化)/C-N(sp3杂化)比例以及明显增加的吡啶氮信号,证实了Co-N_(5)/DHC显著提升的氮掺杂碳缺陷浓度并具有丰富的边界/缺陷位点.同时,X射线吸收谱与球差矫正透射电子显微镜结果表明所制备的样品为原子分散的Co-N_(5)结构,从而证明成功制备了缺陷氮掺杂碳耦合Co-N_(5)位点单原子催化剂.电化学测试结果表明,缺陷氮掺杂碳耦合Co-N_(5)位点后表现较好的ORR性能,半波电位达到0.877 V,明显高于Co-Nx/HC对比样品和商业化Pt/C催化剂.Koutecky-Levich曲线和旋转盘环电极测试结果表明,Co-N_(5)/DHC催化剂的高效4e-反应路径.且在10000次的加速老化测试中,Co-N_(5)/DHC半波电位仅降低了7 m V,稳定性优于Pt/C.以Co-N_(5)/DHC为阴极催化剂组装的ZAB开路电压为1.45 V,峰值输出功率密度能够达到160.7 m W cm^(-2),并能提供766.2 m A h gZn-1的比容量,展现出较高的应用前景.密度泛函理论计算表明,Co-N_(5)位点与缺陷氮掺杂碳的相互作用诱导Co中心位点电子的重新分布,降低了ORR反应能垒.综上,本文为设计与合成高性能的Co单原子催化剂,用于先进的可再生能源转换系统提供了一种新思路.

Bottom-up lithium growth guided by Ag concentration gradient in 3D PVDF framework towards stable lithium metal anode

Three-dimensional(3 D)frameworks have received much attention as an effective modification strategy for next-generation high-energy-density lithium metal batteries.However,the top-growth mode of lithium(Li)on the 3 D framework remains a tough challenge.To achieve a uniform bottom-up Li growth,a scheme involving Ag concentration gradient in 3 D PVDF framework(C-Ag/PVDF)is proposed.Ag nanoparticles with a concentration gradient induce an interface activity gradient in the 3 D framework,and this gradient feature is still maintained during the cycle.As a result,the C-Ag/PVDF framework delivers a long lifespan over 1800 h at a current density of 1 mA cm^(-2) with a capacity of 1 mAh cm^(-2),and shows an ultra-long life(>1300 h)even at a high current density of 4 mA cm^(-2) with a capacity of 4 mAh cm^(-2).The advantage of concentration gradient provides further insights into the optimal design of the 3 D framework for stable Li metal anode.

Recent Advances in 2D Lateral Heterostructures

Recent developments in synthesis and nanofabrication technologies offer the tantalizing prospect of realizing various applications from twodimensional(2D)materials.A revolutionary development is to flexibly construct many different kinds of heterostructures with a diversity of 2D materials.These 2D heterostructures play an important role in semiconductor and condensed matter physics studies and are promising candidates for new device designs in the fields of integrated circuits and quantum sciences.Theoretical and experimental studies have focused on both vertical and lateral 2D heterostructures;the lateral heterostructures are considered to be easier for planner integration and exhibit unique electronic and photoelectronic properties.In this review,we give a summary of the properties of lateral heterostructures with homogeneous junction and heterogeneous junction,where the homogeneous junctions have the same host materials and the heterogeneous junctions are combined with different materials.Afterward,we discuss the applications and experimental synthesis of lateral 2D heterostructures.Moreover,a perspective on lateral 2D heterostructures is given at the end.

Li/C composites as anodes for high energy density rechargeable Li batteries

Current lithium (Li) ion batteries consisting of graphite as the anode and intercalation materials (such as LiCoO2, LiNixCoyMn1-x-yO2, LiNi0.8Co0.1Al0.1O2) as the cathodes have almost reached their theoretical energy density of 300 Wh/kg. As a result, exploring high energy density batteries is urgent. Li-metal taking place of the graphite as the anode has several advantages. On one hand, it has a low operational voltage (-3.04 V versus standard hydrogen electrode) and a high specific capacity of 3860 mAh/g offering the battery with high energy density. On the other hand, when the Li-metal as the anode, the cathodes can be extended to Li-free or Li-deficient materials, which means the cathodes have more choices. For instance, S, O2, conversion reaction-type materials can be optional. While, the introduction of Li-metal anodes brings in several challenges [1–3]. Firstly, Li-metal is highly electrochemical and electrochemical active to have undesirable reactions with conventional carbonate-based liquid electrolytes, leading a low Coulombic efficiency and large polarizations. Secondly, the formed Li dendrites due to uneven Li+ distribution during plating and stripping has the chances of percolating separators leading to short circuits. Thirdly, Li metal is a host-free material (~5 μm have a capacity of 1 mAh/cm2), thus it suffers from a huge volume change, which brings in difficulty in the cell design.

Vacancy defect modulation in hot-casted NiOx film for efficient inverted planar perovskite solar cells

Nickel oxide(NiOx)has exhibited great potential as an inorganic hole transport layer(HTL)in perovskite solar cells(PSCs)due to its wide optical bandgap and superior stability.In this study,we have modulated the Ni26 vacancies in NiOx film by controlling deposition temperature in a hot-casting process,resulting the change of coordination structure and charge state of NiOx.Moreover,the change of the HOMO level of NiOx makes it more compatible with perovskite to decrease energy losses and enhance hole carrier injection efficiency.Besides,the defect modulation in the electronic structure of NiOx is beneficial for increasing the electrical conductivity and mobility,which are considered to achieve the balance of charge carrier transport and avoid charge accumulation at the interface between perovskite and HTL effectively.Both experimental analyses and theoretical calculations reveal the increase of nickel vacancy defects change the electronic structure of NiOx by increasing the ratio of Ni3^+/Ni2^+-and improving the p-type characteristics.Accordingly,an optimal deposition temperature at 120℃enabled a 36.24%improvement in the power conversion efficiency compared to that deposited at room temperature(25℃).Therefore,this work provides a facile method to manipulate the electronic structure of NiOx to improve the charge carrier transport and photovoltaic performance of related PSCs.

Misfit strains inducing voltage decay in LiMn_(y)Fe_(1-y)PO_(4)/C

LiMn_(y)Fe_(1-y)PO_(4) is considered a promising cathode material for next-generation lithium-ion batteries(LIBs) due to its high energy density and low cost. Its energy density degradation is often ascribed to the capacity loss during cycling. However, in this study, we find that the energy density degradation mainly roots in voltage decay. We have synthesized a series of LiMn_(y)Fe_(1-y)PO_(4) /C(0.5 ≤ y ≤ 0.8) and find this voltage decay is correlated with the Mn content. A high amount Mn leads to a heavier voltage decay.In-situ X-ray diffraction(XRD) and high-resolution transmission electron microscopy(HRTEM) reveal the nature of this effect, which show a mismatch along the b-axis of-2.68%(charge) and +3.4%(discharge), a volume misfit of-4.41%(charge) and +4.54%(discharge) between Li_(x)Mn_(y)Fe_(1-y)PO_(4) and Mn_(y)Fe_(1-y)PO_(4) during phase transitions. The resultant misfit strains during Li+insertion compared to extraction result in structural degradations, such as amorphization and impurity(Mn F3) accumulation after cycling. The voltage decay can be alleviated by kinetic relaxations and recovered by a wild reannealing. This work demonstrates effective strategies to improve the energy density and cycling performance of LiMn_(y)Fe_(1-y)PO_(4) /C,providing good references for other LIB cathodes, such as the Li-rich cathodes.

Facile lattice tensile strain compensation in mixed-cation halide perovskite solar cells

Despite the rapid development of power conversion efficiency(PCE)for halide perovskite solar cells(PSCs),the lattice strain engineering in perovskite thin films has been rarely probed in recent years.Herein,a strain compensation by homogeneous crystallization in perovskite films is achieved with the aid of precursor aging in the mixed-cation perovskite of Cs_(0.05)(FA_(0.83)MA_(0.17))Pb(I_(0.90)Br_(0.10))_(3)with near 20%PCE in inverted devices.The homogeneous crystallization releases the residual tensile stress and induces more compressive stress at the edges of perovskite films,thus elongating the carrier lifetime and reducing the trap-assisted carrier recombination.The high dependence on the perovskite components in strain engineering strategy was systematically revealed,wherein MAPbI_(3)and Cs_(0.05)(FA_(0.83)MA_(0.17))PbI_(3)film showed an increased compressive strain and FAPbI3 film showed adverse tensile strain after aging.The density functional theory(DFT)calculations are further performed to reveal the change of electronic features.The precursor aging-induced strain modulation was correlated with a systematic characterization of the charge carrier transport and recombination dynamics in the mixed-cation perovskite films.We believe that this facile approach provides a novel strain engineering strategy for PSCs technology.

Tailoring the interactions of heterostructured Ni_(4)N/Ni_(3)ZnC_(0.7)for efficient CO_(2)electroreduction

Electrocatalytic CO_(2)reduction into CO has been regarded as one of the most promising strategies for sustainable carbon cycles at ambient conditions,but still faces challenges to achieve both high product selectivity and large current density.Here,we report a Ni_(4)N/Ni_(3)ZnC_(0.7)heterostructured electrocatalyst embedded in accordion-like N-doped carbon through a simple molten salt annealing strategy.The optimal Ni_(4)N/Ni_(3)ZnC_(0.7)electrocatalyst achieves a high CO Faraday efficiency of 92.3%and a large total current density of-15.8 m A cm^(-2)at-0.8 V versus reversible hydrogen electrode,together with a long-term stability about 30 h.Density functional theory results reveal that the energy barrier for*COOH intermediate formation largely decreased on Ni_(4)N/Ni_(3)ZnC_(0.7)heterostructure compared with Ni_(4)N and Ni_(3)ZnC_(0.7),thus giving rise to enhanced activity and selectivity.A rechargeable Zn-CO_(2)battery is further assembled with Ni_(4)N/Ni_(3)ZnC_(0.7)catalyst as the cathode,which shows a maximum power density of 0.85 mW cm^(-2)and excellent stability.

Monolithic epitaxy and optoelectronic properties of single-crystalline γ-In_(2)Se_(3) thin films on mica

The growth of γ-In_(2)Se_(3) thin films on mica by molecular beam epitaxy is studied. Single-crystalline γ-In_(2)Se_(3) is achieved at a relatively low growth temperature. An ultrathin β-In_(2)Se_(3) buffer layer is observed to nucleate and grow through a process of self-organization at initial deposition, which facilitates subsequent monolithic epitaxy of single-crystallineγ-In_(2)Se_(3) at low temperature. Strong room-temperature photoluminescence and moderate optoelectronic response are observed in the achieved γ-In_(2)Se_(3) thin films.

FeSO_(4) as a Novel Li-Ion Battery Cathode

FeSO_(4) has the characteristics of low cost and theoretical high energy density(799 W·h·kg^(-1) with a two-electron reaction),which can meet the demand for next-generation lithium-ion batteries.Herein,FeSO_(4) as a novel highperformance conversion-reaction type cathode is investigated.We use dopamine as a carbon coating source to increase its electronic conductivity.FeSO_(4)@C demonstrates a high reversible specific capacity(512 mA·h·g^(-1))and a superior cycling performance(482 mA·h·g^(-1) after 250 cycles).In addition,we further study its reaction mechanism.The FeSO_(4) is converted to Fe and Li2SO_(4) during lithium ion insertion and the Fe-Li_(2)SO_(4) grain boundaries further store additional lithium ions.Our findings are valuable in exploring other new conversion-type lithium ion battery cathodes.

In-situ construction of Li4Ti5O12/rutile TiO2 heterostructured nanorods for robust and high-power lithium storage

Li4Ti5O12 is considered as a safe and stable anode material for high-power lithium-ion batteries due to its“zero-strain”characteristic during the charge/discharge.However,the intrinsically low electronic conductivity leads to a deterioration in highrate performance,impeding its intensive application.Herein,the Li4Ti5O12/rutile TiO2(LTO/RT)heterostructured nanorods with tunable oxide phases have been in-situ fabricated by annealing the electrospun nanofiber precursor.By constructing such a heterostructured interface,the as-prepared sample delivers a high capacity of 160.3 mAh·g–1 at 1 C after 200 cycles,125.5 mAh·g–1 at 10 C after 500 cycles and a superior capacity retention of 90.3%after 1,000 cycles at 30 C,outperforming the heterostructure-free counterparts of pure LTO,RT and the commercial LTO product.Density Functional Theory calculation suggests a possible synergistic effect of the LTO/RT interface that would improve the electronic conductivity and Li-ion diffusion.

Copper diffusion related phase change and voltage decay in CuS cathode

Copper sulfide(CuS)is a promising cathode for lithium-ion batteries(LIBs)due to its impeccable theoretical energy density(~1015 Wh·kg^(−1) and 4743 Wh·L^(−1)).However,it suffers from voltage decay leaded energy density loss and low energy efficiency,which hinders its application.In this work,with combined ex-situ/in-situ X-ray diffraction(XRD)and electrochemical analysis,we explore detailed degradation mechanisms.For the voltage decay,it is attributed to a spontaneous reaction between CuS cathode and copper current collector(Cu CC).This reaction leads to energy density loss and active materials degradation(CuS→Cu_(1.81)S).As for energy efficiency,CuS undergoes a series of phase transformations.The main phase transition processes are CuS→α-LiCuS→Li_(2−x)Cu_(x)S+Cu→Li_(2)S+Cu for discharge;Li_(2)S+Cu→Li_(2−x)Cu_(x)S→β-LiCuS→CuS for charge.Here,α-LiCuS,β-LiCuS,and Li_(2−x)CuxS are newly identified phases.These phase changes are driven by topotactic-reaction-related copper diffusion and rearrangement.This work demonstrates the significance of transition-metal diffusion in the intermediates formation and phase change in conversion-type materials.

Multifunctional anchoring of O-ligands for high-performance and stable inverted perovskite solar cells

Functional additives have recently been regarded as emerging candidates to improve the performance and stability of perovskite solar cells(PSCs).Herein,nicotinamide(N),2-chloronicotinamide(2Cl),and 6-chloronicotinamide(6Cl)were employed as O-ligands to facilitate the deposition of MAPbI_(3)(MA=methylammonium)and MA-free FA_(0.88)Cs_(0.12)PbI_(2.64)Br_(0.36)(FA=formamidinium)perovskite films by multifunctional anchoring.By density functional theory(DFT)calculations and ultraviolet photoelectron spectroscopy(UPS)measurements,it is identified that the highest occupied molecular orbital(HOMO)level for additive modified MAPbI_(3)perovskite could reduce the voltage deficit for hole extraction.Moreover,due to the most favorable charge distribution and significant improvements in charge mobility and defect passivation,the power conversion efficiency(PCE)of 2Cl-MAPbI_(3)PSCs was significantly improved from 19.32%to 21.12%.More importantly,the two-dimensional grazing-incidence wide-angle X-ray scattering(GIWAXS)analysis showed that PbI_(2) defects were effectively suppressed and femtosecond transient absorption(TA)spectroscopy demonstrated that the trap-assisted recombination at grain boundaries was effectively inhibited in the 2Cl-MA-free film.As a result,the thermally stable 2Cl-MA-free PSCs achieved a remarkable PCE of 23.13%with an open-circuit voltage(V_(oc))of 1.164 V and an ultrahigh fill factor(FF)of 85.7%.Our work offers a practical strategy for further commercializing stable and efficient PSCs.

Stabilizing highly active atomically dispersed NiN_(4)Cl sites by Cl-doping for CO_(2)electroreduction

Nickel-nitrogen-carbon single-atom catalysts have attracted widespread interest for CO_(2)electroreduction but they suffer from poor stability.Herein,we report on the preparation of Cl-and N-doped porous carbon nanosheets with atomically dispersed NiN_(4)Cl active sites(NiN_(4)Cl-ClNC)through a molten-salt-assisted pyrolysis strategy.The optimized NiN_(4)Cl-ClNC catalyst delivers exceptional CO_(2)conversion activity with outstanding stability for over 220 h at−0.7 V versus RHE and a high CO Faradaic efficiency of 98.7%at a CO partial current density of 12.4 mA cm^(−2).Moreover,NiN_(4)Cl-ClNC displays a remarkable CO partial current density of approximately 349.4 mA cm^(−2)in flow-cell,meeting the requirements of industrial applications.Operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy and density functional theory calculations are used to understand the outstanding activity and stability.Results reveal that the introduced axial Ni-Cl bond on the Ni center and Cl─C bond on the carbon support synergetically induce electronic delocalization,which not only stabilizes Ni against leaching but also facilitates the formation of the COOH*intermediate that is found to be the rate-determining step.

Atomic-scale structural and chemical evolution of Li3V2(PO4)3 cathode cycled at high voltage window

Here,by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy,we investigate the structural and chemical evolution of Li3V2(PO4)3 (LVP) upon the high-voltage window (3.0-4.8 V).We find that the valence of vanadium gradually increases towards the core corresponding to the formation of electrochemically inactive Li3-xV2(PO4)3 (L3-xVP) phases.These Li-deficient phases exhibit structure distortion with superstructure stripes,likely caused by the migration of the vanadium,which can slow down the lithium ion diffusion or even block the diffusion channels.Such kinetic limitations lead to the formation of Li-deficient phase along with capacity loss.Thus,the LVP continuously losses of electrochemical activity and Li-deficient phases gradually grow from the particle core towards the surface during cycling.After 500 cycles,the thickness of active LVP layer decreases to be - 5-20 nm.Moreover,the micromorphology and chemical composition of solid electrolyte interphase (SEI) have been investigated,indicating the thick SEI film also contributes to the capacity loss.The present work reveals the structural and chemical evolution in the cycled electrode materials at an atomic scale,which is essential to understand the voltage fading and capacity decaying of LVP cathode.

Criteria for the growth of large-area adlayer-free monolayer graphene films by chemical vapor deposition

Homogeneity is important to material applications for good performance of individual devices,for making AB-stacked bilayer graphene in a layer-by-layer stacking order,and from the point of view of industrial production.Among many properties to be controlled,for the case of graphene,the thickness(or layer number)uniformity is the prerequisite.Chemical vapor deposition(CVD)of C precursors on Cu substrates is the most popular method to produce large-area graphene films.To date,precise control on the number of graphene layers as well as the uniformity over a large area is still very challenging.In this work,with a further understanding of the factors affecting adlayer growth,the synthesis of large-area adlayer-free monolayer graphene(MLG)films was achieved up to tens of squared centimeters in area by just using untreated Cu foil and a normal CVD process.We found that keeping equal C precursor concentration on the two sides of the Cu substrate is a criterion in addition to other factors such as the ratio of H:C and the substrate surface morphology for the growth of adlayer-free MLG.This finding is not only of great significance for the industrial production of large-area adlayer-free MLG films but also instructive for the synthesis of homogeneous few-layer graphene.

Epitaxial growth and thermal-conductivity limit of singlecrystalline Bi2Se3/In2Se3 superlattices on mica

在超点阵的热运输被各种各样的散布声子的过程管理。为在 chalcogenide 超点阵提取异种接口的散布声子的贡献，单人赛水晶的双性人 2 Se 3/In2 有最小化的缺点的 Se 3(BS/IS ) 超点阵被分子的横梁取向附生在 fluorophlogopite 云母上准备。BS/IS 超点阵的跨飞机的进行热的性质被表明精确取决于时期厚度和超点阵的成分，在在热传导性的最小显示一条转线路从的地方对在超点阵的像波浪的声子运输像粒子。BS/IS 超点阵的热传导性的最小比内在的 BS 电影的低将近一个数量级。

Highly Efficient Na+ Storage in Uniform Thorn Ball-Like α-MnSe/C Nanospheres

Because of its high theoretical capacity,MnSe has been identified as a promising candidate as the anode material for sodiumion batteries.However,its fast capacity deterioration due to the huge volume change during the intercalation/deintercalation of sodium ions severely hinders its practical application.Moreover,the sodium storage mechanism of MnSe is still under discussion and requires in-depth investigations.Herein,the unique thorn ball-likeα-MnSe/C nanospheres have been prepared using manganese-containing metal organic framework(Mn-MOF)as a precursor followed by in situ gas-phase selenization at an elevated temperature.When serving as the anode material for sodium-ion battery,the as-preparedα-MnSe/C exhibits enhanced sodium storage capabilities of 416 and 405 mAh g^(-1)at 0.2 and 0.5 A g^(-1)after 100 cycles,respectively.It also shows a superior capacity retention of 275 mA h g^(-1)at 10 A g^(-1)after 2000 cycles,and a rate performance of 279 mA h g^(-1)at 20 A g^(-1).Such sodium storage properties could be attributed to the unique structure offering a highly efficient Na+diffusion kinetics with a diffusion coefficient between 1×10^(-11) and 3×10^(-10) cm^(2) s-1.The density functional theory calculation indicates that the fast Na+diffusion mainly takes place on the(100)plane of MnSe along a V-shaped path because of a relatively low diffusion energy barrier of 0.15 eV.