Penetrative and migratory behavior of alkali metal in different binder based TiB_2-C composite cathodes

In electrolyte melts containing K at low temperature, the penetrative and migratory path of alkali metals （K and Na） in pitch, furan, phenolic aldehyde and epoxy based TiB2-C composite cathodes during the electrolysis process were studied by EDS and self-made modified Rapoport apparatus. The electrolysis expansion rates, the diffusion coefficients of the alkali metals and the corrosion rates of the composite cathode were also calculated and discussed. The results show that no matter what kind of binder is used, alkali metals have the same penetrative path in composite cathodes：firstly in pore, then in binder and finally in carbonaceous aggregates. K and Na penetrate into both binder and carbonaceous aggregates, which leads to the expansion of composite cathodes, and K has stronger penetration ability than Na. Electrolysis expansion rate of resin based composite cathode is smaller than that of pitch based composite cathodes, and so do the diffusion coefficient and corrosion rate. Resin based composite cathode has better resistance ability to the penetration of alkali metals than pith based composite cathode, and phenolic aldehyde based composite cathode exhibits the strongest resistance ability. The penetration rate, the diffusion coefficient of alkali metals in phenolic aldehyde based TiB2-C composite cathode and the corresponding corrosion rate are 4.72 mm/h, 2.24×10^-5 cm^2/s and 2.31 mm/a, respectively.

Interface engineering for composite cathodes in sulfide-based all-solid-state lithium batteries

All-solid-state lithium battery(ASLB)based on sulfide-based electrolyte is considered to be a candidate for the next-generation high-energy storage system.Despite the high ionic conductivity of sulfide solid electrolyte,the poor interfacial stability(mechanically and chemically)between active materials and sulfide solid electrolytes in composite cathodes leads to inferior electrochemical performances,which impedes the practical application of sulfide electrolytes.In the past years,various of strategies have been carried out to achieve an interface with low impedance in the composite cathodes.Herein,a review of recent progress of composite cathodes for all-solid-state sulfide-based lithium batteries is summarized,including the interfacial issues,design strategies,fabrication methods,and characterization techniques.Finally,the main challenges and perspectives of composite cathodes for high-performance all-solidstate batteries are highlighted for future development.

Fabrication and performance of La(0.8)Sr(0.2)MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer （1 -x）La0.8Sr0.2MnO3/xYSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells （SOFC）. The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The （1 -x）Lao.sSr0.EMnO3/xYSZ composite cathode greatly increased the length of the active triple phase boundary line （TPBL） among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode （0.77 A/cm2） was the highest and that of the monolayer cathode （0.13 A/cm2） was the lowest. The polarization resistance （Rp） of the triple-layer graded composite cathode was only 0.182 Ω·cm2 and that of the monolayer composite cathode was 0.323 Ω·cm2. The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.

Electrochemical performance of La_(1-x)Sr_xCuO_(3-δ)-Sm_(0.15)Ce_(0.85)O_(1.925) composite cathodes in IT-SOFCs

The cathode material La1-xSrxCuO3-δ(x=0.15, 0.2, 0.3, 0.4) was synthesized by a sol-gel method. X-ray diffraction reveals that a single phase of perovskite is formed. The investigation of the electrical properties suggests that La0.7Sr0.3CuO3-δ has the highest electrical conductivity. La0.7Sr0.3CuO3-δ powder was mixed with different amount SDC (Sm0.15Ce0.85O1.925) powder (5wt.%-30wt.%) as composite cathodes. Electrochemical properties of the composite cathodes were researched further. Investigation suggests that the addition of appropriate amount SDC to La0.7Sr0.3CuO3-δ can improve the electrochemical properties and obtain better cathodic performance. Using La0.7Sr0.3CuO3-δ-SDC composite materials as a cathode based on SDC electrolyte, higher current density and power density at intermediate temperatures can be obtained.

Review:Development of lanthanum strontium cobalt ferrite composite cathodes for intermediate-to low-temperature solid oxide fuel cells

Solid oxide fuel cells （SOFCs） offer high energy conversion, low noise, low pollutant emission, and low processing cost. Despite many advantages, SOFCs face a major challenge in competing with other types of fuel cells because of their high operating temperature. The necessity to reduce the operational temperature of SOFCs has led to the development of research into the materials and fabrication technology of fuel cells. The use of composite cathodes significantly reduces the cathode polarization resistance and expands the triple phase boundary area available for oxygen reduction. Powder preparation and composite cathode fabrication also affect the overall performance of composite cathodes and fuel cells. Among many types of cathode materials, lanthanum-based materials such as lanthanum strontium cobalt ferrite （Lal_xSrxCOl_yFey03_~） have recently been discovered to offer great compatibility with ceria-based electrolytes in performing as composite cathode materials for intermediate- to low-temperature SOFCs （IT-LTSOFCs）. This paper reviews various ceria-based composite cathodes for IT-LTSOFCs and focuses on the aspects of progress and challenges in materials technology.

Incorporation of Ionic Conductive Polymers into Sulfide Electrolyte-Based Solid-State Batteries to Enhance Electrochemical Stability and Cycle Life

Sulfide-based inorganic solid electrolytes are promising materials for high-performance safe solid-state batteries.The high ion conductivity,mechanical characteristics,and good processability of sulfide-based inorganic solid electrolytes are desirable properties for realizing high-performance safe solid-state batteries by replacing conventional liquid electrolytes.However,the low chemical and electrochemical stability of sulfide-based inorganic solid electrolytes hinder the commercialization of sulfide-based safe solid-state batteries.Particularly,the instability of sulfide-based inorganic solid electrolytes is intensified in the cathode,comprising various materials.In this study,carbonate-based ionic conductive polymers are introduced to the cathode to protect cathode materials and suppress the reactivity of sulfide electrolytes.Several instruments,including electrochemical spectroscopy,X-ray photoelectron spectroscopy,and scanning electron microscopy,confirm the chemical and electrochemical stability of the polymer electrolytes in contact with sulfide-based inorganic solid electrolytes.Sulfide-based solid-state cells show stable electrochemical performance over 100 cycles when the ionic conductive polymers were applied to the cathode.

Investigation and optimization of high-valent Ta-doped SrFeO_(3-δ)as air electrode for intermediate-temperature solid oxide fuel cells

To explore highly active and thermomechanical stable air electrodes for intermediate-temperature solid oxide fuel cells(ITSOFCs),10mol%Ta5+doped in the B site of strontium ferrite perovskite oxide(SrTa_(0.1)Fe_(0.9)O_(3-δ),STF)is investigated and optimized.The effects of Ta^(5+)doping on structure,transition metal reduction,oxygen nonstoichiometry,thermal expansion,and electrical performance are evaluated systematically.Via 10mol%Ta^(5+)doping,the thermal expansion coefficient(TEC)decreased from 34.1×10^(-6)(SrFeO_(3-δ))to 14.6×10^(-6) K^(-1)(STF),which is near the TEC of electrolyte(13.3×10^(-6) K^(-1) for Sm_(0.2)Ce_(0.8)O_(1.9),SDC),indicates excellent thermomechanical compatibility.At 550-750℃,STF shows superior oxygen vacancy concentrations(0.262 to 0.331),which is critical in the oxygen-reduction reaction(ORR).Oxygen temperature-programmed desorption(O_(2)-TPD)indicated the thermal reduction onset temperature of iron ion is around 420℃,which matched well with the inflection points on the thermos-gravimetric analysis and electrical conductivity curves.At 600℃,the STF electrode shows area-specific resistance(ASR)of 0.152Ω·cm^(2) and peak power density(PPD)of 749 mW·cm^(-2).ORR activity of STF was further improved by introducing 30wt%Sm_(0.2)Ce_(0.8)O_(1.9)(SDC)powder,STF+SDC composite cathode achieving outstanding ASR value of 0.115Ω·cm2 at 600℃,even comparable with benchmark cobalt-containing cathode,Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ)(BSCF).Distribution of relaxation time(DRT)analysis revealed that the oxygen surface exchange and bulk diffusion were improved by forming a composite cathode.At 650℃,STF+SDC composite cathode achieving an outstanding PPD of 1117 mW·cm^(-2).The excellent results suggest that STF and STF+SDC are promising air electrodes for IT-SOFCs.

Viability of all-solid-state lithium metal battery coupled with oxide solid-state electrolyte and high-capacity cathode

Owing to the utilization of lithium metal as anode with the ultrahigh theoretical capacity density of 3860 mA h g^(-1)and oxide-based ceramic solid-state electrolytes(SE),e.g.,garnet-type Li7La_(3)Zr_(2)O_(12)(LLZO),all-state-state lithium metal batteries(ASLMBs)have been widely accepted as the promising alternatives for providing the satisfactory energy density and safety.However,its applications are still challenged by plenty of technical and scientific issues.In this contribution,the co-sintering temperature at 500℃is proved as a compromise method to fabricate the composite cathode with structural integrity and declined capacity fading of LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2)(NCM).On the other hand,it tends to form weaker grain boundary(GB)inside polycrystalline LLZO at inadequate sintering temperature for LLZO,which can induce the intergranular failure of SE during the growth of Li filament inside the unavoidable defect on the interface of SE.Therefore,increasing the strength of GB,refining the grain to 0.4μm,and precluding the interfacial defect are suggested to postpone the electro-chemo-mechanical failure of SE with weak GB.Moreover,the advanced sintering techniques to lower the co-sintering temperature for both NCM-LLZO composite cathode and LLZO SE can be posted out to realize the viability of state-of-the-art ASLMBs with higher energy density as well as the guaranteed safety.

Vapor-grown carbon fibers enhanced sulfur-multi walled carbon nanotubes composite cathode for lithium/sulfur batteries

Vapor-grown carbon fibers （VGCFs） were introduced as conductive additives for sulfur-multiwalled carbon nanotubes （S-MWCNTs） composite cathode of lithium-sulfur batteries. The performance of S-MWCNTs composite cathodes with carbon black and VGCFs as sole conductive additives was investigated using scanning electron microscopy （SEM）, galvanostatic charge-discharge tests and electrochemical impedance spectroscopy （EIS）. The results show that the S-MWCNTs composite cathode with VGCFs displays a network-like morphology and exhibits higher activity and better cycle durability compared with the composite cathode with carbon black, delivering an initial discharge capacity of 1254 mA＆#183;h/g and a capacity of 716 mA＆#183;h/g after 40 cycles at 335 mA/g. The interconnected VGCFs can provide a stable conductive network, suppress the aggregation of cathode materials and residual lithium sulfide and maintain the porosity of cathode, and therefore the electrochemical performance of S-MWCNTs composite cathode is enhanced.

Dry electrode technology for scalable and flexible high-energy sulfur cathodes in all-solid-state lithium-sulfur batteries

All-solid-state lithium-sulfur batteries(ASSLSBs)employing sulfide solid electrolytes are one of the most promising next-generation energy storage systems due to their potential for higher energy density and safety.However,scalable fabrication of sheet-type sulfur cathodes with high sulfur loading and excellent performances remains challenging.In this work,sheet-type freestanding sulfur cathodes with high sulfur loading were fabricated by dry electrode technology.The unique fibrous morphologies of polytetrafluoroethylene(PTFE)binders in dry electrodes not only provides excellent mechanical properties but also uncompromised ionic/electronic conductance.Even employed with thickened dry cathodes with high sulfur loading of 2 mg cm^(-2),ASSLSBs still exhibit outstanding rate performance and cycle stability.Moreover,the all-solid-state lithium-sulfur monolayer pouch cells(9.2 m Ah)were also demonstrated and exhibited excellent safety under a harsh test situation.This work verifies the potential of dry electrode technology in the scalable fabrication of thickened sulfur cathodes and will promote the practical applications of ASSLSBs.

Enhancing interfacial stability in solid-state lithium batteries with polymer/garnet solid electrolyte and composite cathode framework

The solid-state lithium battery is considered as an ideal next-generation energy storage device owing to its high safety,high energy density and low cost.However,the poor ionic conductivity of solid electrolyte and low interfacial stability has hindered the application of solid-state lithium battery.Here,a flexible polymer/garnet solid electrolyte is prepared with poly(ethylene oxide),poly(vinylidene fluoride),Li6.75La3 Zr1.75Ta0.25O12,lithium bis(trifluoromethanesulfonyl)imide and oxalate,which exhibits an ionic conductivity of 2.0 ×10^(-4) S cm^(-1) at 55℃,improved mechanical property,wide electrochemical window(4.8 V vs.Li/Li+),enhanced thermal stabilities.Tiny acidic OX was introduced to inhibit the alkalinity reactions between Li6.75La3 Zr1.75Ta0.25O12 and poly(vinylidene fluoride).In order to improve the interfacial stability between cathode and electrolyte,an Al2 O3@LiNi0.5Co0.2Mn0.3O2 based composite cathode framework is also fabricated with poly(ethylene oxide) polymer and lithium salt as additives.The solid-state lithium battery assembled with polymer/garnet solid electrolyte and composite cathode framework demonstrates a high initial discharge capacity of 150.6 mAh g^(-1) and good capacity retention of 86.7% after 80 cycles at 0.2 C and 55℃,which provides a promising choice for achieving the stable electrode/electrolyte interfacial contact in solid-state lithium batteries.

Structure and Tribological Property of TiBN Nanocomposite Multilayer Synthesized by Ti-BN Composite Cathode Plasma Immersion Ion Implantation and Deposition

A Ti-BN complex cathode is made from Ti and h-BN powders by the powder metallurgy technology, and TiBN coating is obtained by plasma immersion ion implantation and deposition with this Ti-BN composite cathode. The TiBN coating shows a self-forming multilayered nanocomposite structure while with relative uniform elemental distributions. High resolution transmission electron microscopy images reveal that the multilayered structure is derived from different grain sizes in the nanocomposite. Due to the existence of h-BN phase, the friction coefficient of the coating is about 0.25.

Effect of baking processes on properties of TiB_2/C composite cathode material

Pitch and TiB2/C green composite cathode material were respectively analyzed with simultaneous DSC-TGA, and effects of three baking processes of TiB2/C composite cathode material, i.e. K25, K5 and M5, on properties of TiB2/C composite cathode material were investigated. The results show that thermogravimetrie behavior of pitch and TiB2/C green composite cathode is similar, and appears the largest mass loss rate in the temperature range from 200 to 600 ℃. The bulk density variation of sample K5 before and after baking is the largest （11.9%）, that of sample K25 is the second, and that of sample M5 is the smallest （6.7%）. The crushing strength of sample M5 is the biggest （51.2 MPa）, that of sample K2.5 is the next, and that of sample K5 is the smallest （32.8 MPa）. But, the orders of the electrical resistivity and electrolysis expansion of samples are just opposite with the order of crushing strength. The heating rate has a great impact on the microstructure of sample. The faster the heating rate is, the bigger the pore size and porosity of sample are. Compared with the heating rate between 200 and 600℃ of samples K25 and K5, that of sample M5 is slower and suitable for baking process of TiB2/C composite cathode material.

Electrochemical properties of La_(0.8)Sr_(0.2)FeO_(3-δ) based composite cathode for intermediate temperature SOFC

La0.8Sr0.2FeO3-δ is a new kind of cathode material for intermediate SOFC, but its electrochemical activity is relative poor for the lanthanum gallate based solid oxide fuel cell. In this paper, a novel composite cathode of La0.8Sr0.2FeO3-δ/La0.9Sr0.1Ga0.8Mg0.2O3-δ was prepared on the LSGM electrolyte substrate by screen-printing method. The results of cathodic polarization measurements show that the overpotential decreases significantly when the composite cathode is used instead of the La0.8Sr0.2FeO3-δ single layer cathode. The cathodic overpotential of the composite La0.8Sr0.2FeO3-δ/La0.9Sr0.1Ga0.8Mg0.2O3-δ cathode is 150 mV at the current density of 0.2 A·cm-2 at 800 ℃, while the cathodic overpotential of the La0.8Sr0.2FeO3-δ single layer cathode is higher than 260 mV at the same condition. The electrochemical impedance spectroscopy was employed to investigate the polarization resistance of the cathode. The polarization resistance of the composite cathode is 1.20 Ω·cm2 in open circuit condition, while the value of the single La0.8Sr0.2FeO3-δ cathode is 1.235 Ω·cm2.

Composite Cathode Bi_(1.14)Sr_(0.43)O_(2.14)-Ag for Intermediate-temperature Solid Oxide Fuel Cells

Composites consisting of strontium stabilized bismuth oxide （Bi1.14Sr0.43O2.14, SSB） and silver were investigated as cathodes for intermediate-temperature solid oxide fuel cells with doped ceria electrolyte. There were no chemical reactions between the two components. The microstructure of the interfaces between composite cathodes and Ce0.8Sm0.2O1.9 （SDC） electrolytes was examined by scanning electron microscopy （SEM）. Impedance spectroscopy measurements show that the performance of cathode fired at 700 ℃ is the best. When the content of Ag2O is 70 wt%, polarization resistance values for the SSB-Ag cathodes are as low as 0.2 Ωcm^2 at 700℃ and 0.29 Ωcm^2 at 650℃. These results are much smaller than some of other reported composite cathodes on doped ceria electrolyte and indicate that SSB-Ag composite is a potential cathode material for intermediate temperature SOFCs.

Growing Intact Membrane by Tuning Carbon Down to Ultrasmall 0.37 nm Microporous Structure for Confining Dissolution of Polysulfides Toward High-Performance Sodium–Sulfur Batteries

Room temperature sodium–sulfur(Na–S)batteries are severely hampered by dissolution of polysulfides into electrolytes.Herein,a facile approach is used to tune a biomass-derived carbon down to an ultrasmall 0.37 nm microporous structure for the first time as a cathode in sodium–sulfur batteries.This produced an intact uniform Na2S membrane to greatly confine the dissolution of polysulfides while realizing a direct solid phase conversion for complete reduction of sulfur to Na2S,which delivers a sulfur loading of 1 mg cm−2(50 wt.%),an excellent rate capacity(933 mAh g^(−1)@0.1 A g^(−1)and 410 mAh g^(−1)@2Ag^(−1)),long cycle performance(0.036%per cycle decay at 1 A g^(−1)after 1500 cycles),and a high energy density for 373 Wh kg^(−1)(0.1 A g^(−1))based on whole electrode weight(active sulfur loading+carbon),ranking the best among all reported plain carbon cathode-based room temperature sodium–sulfur batteries in terms of the cycle life and rate capacity.It is proposed that the solid Na2S produced in the ultrasmall pores(0.37 nm)can be squeezed out to grow an intact membrane on the electrode surface covering the outlet of the pores and greatly depressing the dissolution effect of polysulfides for the long cycle life.This work provides a green chemistry to recycle wastes for sustainable energies and sheds light on design of a unique pore structure to effectively block the dissolution of polysulfides for high-performance sodium–sulfur batteries.

Interface enhanced well-dispersed Co9S8 nanocrystals as an efficient polysulfide host in lithium–sulfur batteries

The high specific capacity and energy density of lithium-sulfur batteries have attracted strong considerations on their fundamental mechanism and energy applications.However,polysulfide shuttle is still the key issue that impedes the development of Li-S batteries.Exploring nanocrystal hosts for polysulfide immobilization and conversion is a promising way.In this contribution,we have investigated well-dispersed Co9S8 nanocrystals grown on graphene oxide(GO)nanosheets with different degrees of dispersion as cathode host materials for Li-S batteries.The Co9S8-GO composite with 1 wt%GO(GCS1)has an average crystal size of 76 nm and shows the strongest adsorption capability toward lithium polysulfides.When used as the host material for the cathode of Li-S batteries,the GCS1-sulfur composite exhibits an initial specific capacity of^-1000 mAh g^-1 at 0.5 C and shows an average decay rate of 0.11%for 500 cycles.This work on the dispersion control of Co9S8 nanocrystals may inspire more investigations on well-dispersed nanocrystal based hosts for Li-S batteries.

Beta-Cyclodextrin as Carbon Source for Synthesis of LiFePO_4/C with Improved Electrochemical Properties in Lithium-ion Batteries

For beta-cyclodextrin (β-CD) may form complexes with metal ions during ballmilling process, it was used as a novel carbon source to synthesize LiFePO_4/C cathode composite in lithium-ion batteries via solid-state reaction. This composite should has fine particle size and good electrochemical performances. The powders were characterized by XRD, SEM, TEM and galvanostatic charge-discharge. Compared with bare LiFePO_4 and LiFePO_4/C composite with glucose as carbon source by the same procedure and nearly the same content of carbon in the final cathode, the LiFePO_4/C composite with beta-cyclodextrin as carbon source shows much higher discharge specific capacity and more excellent rate performance. Ultrasonic dispersion between ballmilling and sinter process for 2 h was appropriate and useful for final LiFePO_4/C to reach higher discharge capacity. The SEI experiment was carried out to explore the effect of beta-cyclodextrin on the cathode materials, and the results indicate that coating with beta-cyclodextrin can improve the electrochemical performance of LiFePO_4 by decreasing the resistance of charge transfer (R_ ct) and improving the chemical diffusion coefficient (D_ Li).

Enhanced Cathode/Electrolyte Interface in Solid-state Li-metal Battery based on Garnet-type Electrolyte

Li/garnet/LiFePO_(4) solid-state battery was fabricated.The cathode contains LiFePO_(4),Ketjen black,poly(vinylidene fluoride):LiTFSI polymer as active material,electric conductor and Li-ion conducting binder,respectively.Polyvinylpyrrolidone was added into the cathode to improve cathode/electrolyte interfacial performance.When combined with polyvinylpyrrolidone additive,poly(vinylidene fluoride):polyvinylpyrrol idone:LiTFSI blend forms,and the cathode/electrolyte interfacial resistance reduces from 10.7 kΩto 3.2 kΩ.The Li/garnet/LiFePO_(4) solid-state battery shows 80%capacity retention after 100 cycles at 30℃and 0.05 C.This study offers a general strategy to improve cathode/electrolyte interfacial performance and may enable the practical application of solid-state Li-metal batteries.

26-electrons redox-active polyoxovanadate clusters for aqueous zincion batteries

Aqueous zinc-ion batteries(ZIBs)are attaining increasing attention for their high safety and low cost.Despite significant progresses in realizing high-performance cathode material for ZIBs,simultaneously endowing them with high capacity and fast-charging capability,the long-term cycling stability remains a major unsolved challenge.In this work,a polyoxovanadate cluster of(NH_(4))_(8)[V_(19)O_(41)(OH)_(9)]·11H_(2)O(NOV)is defined as a cathode material for ZIBs that contains mixed-valence vanadium sites(V^(4+)and V^(5+)).A maximum of 26 electrons can be accommodated in one[V_(19)O_(41)(OH)_(9)]^(8-){V_(19)O_(50)}cluster,contributing to the high theoretical specific capacity of 328 mA·h·g^(-1).The Ti_(3)C_(2)T_(x) MXene nanosheets are incorporated into NOV with the help of ionic liquid(IL)linkers to restrain the dissolution of vanadium species and facilitate electron transport across the electrode.The interfacial bonding,anion exchange,and electrostatic interactions among NOV and MXene are provided by IL liquid.The nanohybrid of NOV-IL-MXene endows excellent contact between MXene and NOV,thereby enhanced charge transfer is observed at interface.Subsequently,the as-synthesized NOV-IL-MXene cathodes exhibit high discharge capacity of 413 mA·h·g^(-1) at 0.2 A·g^(-1) even at high mass loading of 5.2 mg·cm^(-2),remarkable rate performance of 182 mA·h·g^(-1) at 10 A·g^(-1),and impressive cycling stability of 94%capacity retention after 2000 cycles.This work opens up new opportunities to develop advanced polyoxovanadate hybrid cathodes for low-cost and high-performance aqueous ZIBs.