Due to its low cost and natural abundance of sodium,Na-ion batteries(NIBs)are promising candidates for large-scale energy storage systems.The development of ultralow voltage anode materials is of great significance in...Due to its low cost and natural abundance of sodium,Na-ion batteries(NIBs)are promising candidates for large-scale energy storage systems.The development of ultralow voltage anode materials is of great significance in improving the energy density of NIBs.Low-voltage anode materials,however,are severely lacking in NIBs.Of all the reported insertion oxides anodes,the Na_(2)Ti_(3)O_(7) has the lowest operating voltage(an average potential of 0.3 V vs.Na^(+)/Na)and is less likely to deposit sodium,which has excellent potential for achieving NIBs with high energy densities and high safety.Although significant progress has been made,achieving Na_(2)Ti_(3)O_(7) electrodes with excellent performance remains a severe challenge.This paper systematically summarizes and discusses the physicochemical properties and synthesis methods of Na_(2)Ti_(3)O_(7).Then,the sodium storage mechanisms,key issues and challenges,and the optimization strategies for the electrochemical performance of Na_(2)Ti_(3)O_(7) are classified and further elaborated.Finally,remaining challenges and future research directions on the Na_(2)Ti_(3)O_(7) anode are highlighted.This review offers insights into the design of high-energy and high-safety NIBs.展开更多
The low O^(2-)diffusion rate in the electro-deoxidation of titanium containing compounds by either the OS process or the FFC process leads to a low reaction speed and a low current efficiency.In this study,Ca_(3)Ti_(2...The low O^(2-)diffusion rate in the electro-deoxidation of titanium containing compounds by either the OS process or the FFC process leads to a low reaction speed and a low current efficiency.In this study,Ca_(3)Ti_(2)O_(7) was used as a precursor to improve the reduction speed of titanium.Because of the greater number of"diffusion channels"created in cathode as Ca^(2+) liberates from Ca_(3)Ti_(2)O_(7) precursor in the electrodeoxidation process,the O^(2-)diffusion rate was improved significantly by using Ca_(3)Ti_(2)O_(7) instead of CaTiO3 as precursor.Parallel constant voltage electrolysis(3.2 V)confirms that Ca_(3)Ti_(2)O_(7) and CaTiO3 are reduced simultaneously because of their similar crystal structures.However,the reduction area of Ca_(3)Ti_(2)O_(7) spreads much faster than that of CaTiO3,indicating a difference in the O^(2-) diffusion rate.Constant voltage cyclic voltammetry(CV)and theoretical analysis of the crystal structure were also conducted to compare the differences between Ca_(3)Ti_(2)O_(7) and CaTiO3.The results indicate that using a precursor with a greater number of soluble cations,titanium reduction speed can be greatly improved in the electro-deoxidation process.Finally,a new electrolysis method for converting and recycling excess CaO from the Ca_(3)Ti_(2)O_(7) precursor was proposed.展开更多
Na2Ti3O7 has attracted much attention in the field of anode materials for Na-ion batteries thanks to its non-toxicity and very low working potential of 0.3 V vs Na0/Na+.Building a clearer picture of its formation from...Na2Ti3O7 has attracted much attention in the field of anode materials for Na-ion batteries thanks to its non-toxicity and very low working potential of 0.3 V vs Na0/Na+.Building a clearer picture of its formation from cheap Na_(2)CO_(3) and TiO_(2) starting materials is therefore of obvious interest.Here,we report new insights from an in-situ high temperature X-ray diffraction study conducted from room temperature to 800°C,complemented by ex-situ characterizations.We were thereby able to position the previously reported Na_(4)Ti_(5)O_(12) and Na_(2)Ti_(6)O_(13) intermediate phases in a reaction scheme involving three successive steps and temperature ranges.Shifts and/or broadening of a subset of the Na_(2)Ti_(6)O_(13) reflections suggested a combination of intra-layer disorder with the well-established ordering of successive layers.This in-situ study was carried out on reproducible mixtures of Na_(2)CO_(3) and TiO_(2) in 1:3 molar ratio prepared by spraydrying of mixed aqueous suspensions.Single-phase Na_(2)Ti_(3)O_(7) was obtained after only 8 h at 800°C in air,instead of a minimum of 20 h for a conventional solid-state route using the same precursors.Microstructure analysis revealed~15 mm diameter granules made up from rectangular rods of a fewmm length presenting electrochemical properties in line with expectations.In the absence of grinding or formation of intimate composites with conductive carbon,the specific capacity of 137 m Ah/g at C/5 decreased at higher rates.展开更多
A red-emitting phosphor Ca_(2.91)Si_(2)O_(7):0.09Eu^(3+) with partial Al^(3+)/P^(5+) substitution on Si^(4+) was synthesized via a simple solid-state method,and the effects of the introduction of the M^(3+/5+)(M=Al,P)...A red-emitting phosphor Ca_(2.91)Si_(2)O_(7):0.09Eu^(3+) with partial Al^(3+)/P^(5+) substitution on Si^(4+) was synthesized via a simple solid-state method,and the effects of the introduction of the M^(3+/5+)(M=Al,P)ions on the crystal structure and photoluminescence performance of Ca_(2.91)Si_(2−x)M_(x)O_(7):0.09Eu^(3+) phosphors were investigated.The X-ray diffraction(XRD),energy-dispersive X-ray spectroscopy(EDS),and X-ray photoelectron spectroscopy(XPS)results revealed that the structure of Ca_(3)Si_(2)O_(7) remained the same after the introduction of Al^(3+) and P^(5+) ions.The characteristic emission of Eu^(3+)-doped Ca_(3)Si_(2−x)M_(x)O_(7) phosphors exhibited two main peaks at 617 nm(red)and 593 nm(orange)under excitation at 394 nm,which originated from the^(5)D_(0)→^(7)F_(2)and^(5)D_(0)→^(7)F_(1) electron transitions of Eu^(3+) ions.After the partial substitution of Al^(3+) and P^(5+),the red emission intensities of the Ca_(2.91)Si_(2)O_(7):0.09Eu^(3+) phosphors were significantly enhanced by 1.88-and 1.42-fold,respectively,which is attributed to the crystal-field effect around Eu^(3+).Meanwhile,the luminescence intensities of the Ca_(2.91)Si_(1.96)Al_(0.04)O_(7):0.09Eu^(3+) and Ca_(2.91)Si_(1.94)P_(0.06)O_(7):0.09Eu^(3+) phosphors at 210℃ were 79.36%and 77.53%of those at 30°C,respectively,indicating their excellent thermal stability.Moreover,the as-prepared Ca_(2.91)Si_(1.96)Al_(0.04)O_(7):0.09Eu^(3+)and Ca_(2.91)Si_(1.94)P_(0.06)O_(7):0.09Eu^(3+) red-emitting phosphors were combined with a near-ultraviolet chip of 395 nm to fabricate red-light-emitting diode(LED)and white(w)-LED devices with excellent chromaticity features.In summary,Al^(3+)/P^(5+)-substituted Ca_(2.91)Si_(2)O_(7):0.09Eu^(3+) can serve as red-emitting phosphors for applications in w-LEDs.展开更多
Transparent phosphor ceramics have received increasing attention for high-brightness laser lighting,but commercially available phosphor ceramics are currently mainly limited to yellow YAG:Ce and green LuAG:Ce garnets,...Transparent phosphor ceramics have received increasing attention for high-brightness laser lighting,but commercially available phosphor ceramics are currently mainly limited to yellow YAG:Ce and green LuAG:Ce garnets,leaving a“cyan cavity”which is an obstacle to realizing full-color lighting.Achieving new phosphor ceramics capable of filling the cavity is a challenge.Herein,for the first time,cyan-green-emitting Ca_(3)Sc_(2)Si_(3)O_(12):Ce^(3+)(CSS:Ce)transparent ceramics have been successfully developed by two-step sintering technique under vacuum.The as-prepared CSS:Ce ceramics present high relative density of 99.7%and optical transmittance of 71%in the cyan-green spectral region.It exhibits an efficient band emission peaking at 504 nm(under 450 nm excitation)with internal/external quantum efficiency of 91%/62%.Furthermore,it has excellent thermal stability with a thermal quenching temperature(T_(0.5))of 838 K,approximately 100 K higher than that of LuAG:Ce ceramics(738 K).In addition,the CSS:Ce ceramics can withstand blue laser density of 45.6 W/mm^(2)and meanwhile generates cyan-green light with a forward luminous flux of 813 lm and forward luminous efficacy of 162 lm/W.The CSS:Ce transparent ceramics exhibit excellent luminescence performance comparable to the commercial LuAG:Ce ceramics and could be a highly promising color converter for high-brightness laser lighting.展开更多
Ca_(3)Ti_(2)O_(7) with Ruddlesden-Popper structure exhibits the largest polarization among the known hybrid improper ferroelectrics.However,the high Curie temperature impedes the thorough study of phase transition thr...Ca_(3)Ti_(2)O_(7) with Ruddlesden-Popper structure exhibits the largest polarization among the known hybrid improper ferroelectrics.However,the high Curie temperature impedes the thorough study of phase transition through dielectric characterization.According to the previous theoretical design rule,the Curie temperature can be suppressed by increasing the tolerance factor.So,in the present work,high-quality Ca_(3-x)LaxTi_(2-x)Al_(x)O_(7)(x=0.0,0.1,0.2,0.3)ceramics with increased tolerance factors were successfully prepared.The amplitude of oxygen octahedral tilt mode indeed decreases with increasing tolerance factors,leading to a degeneration of ferroelectric polarization.However,the unexpected rigid rotation mode causes the composition-invariable coercive fields.The Curie temperatures decrease linearly with increasing x and tolerance factors.The variable-temperature dielectric constant confirms first-order improper ferroelectric transitions in Ca_(3)Ti_(2)O_(7)-based ceramics.The results of variable temperature Xray diffraction reveal the coexistence of two-phases below Curie temperature.The present work confidently confirms the first-order improper ferroelectric transition in Ca_(3)Ti_(2)O_(7)-based ceramics by combining results of variable-temperature dielectric response and in-situ X-ray powder diffraction.展开更多
基金supported by the National Natural Science Foundation of China (52307239,52102300,52207234)the Natural Science Foundation of Hubei Province (2022CFB1003,2021CFA025)。
文摘Due to its low cost and natural abundance of sodium,Na-ion batteries(NIBs)are promising candidates for large-scale energy storage systems.The development of ultralow voltage anode materials is of great significance in improving the energy density of NIBs.Low-voltage anode materials,however,are severely lacking in NIBs.Of all the reported insertion oxides anodes,the Na_(2)Ti_(3)O_(7) has the lowest operating voltage(an average potential of 0.3 V vs.Na^(+)/Na)and is less likely to deposit sodium,which has excellent potential for achieving NIBs with high energy densities and high safety.Although significant progress has been made,achieving Na_(2)Ti_(3)O_(7) electrodes with excellent performance remains a severe challenge.This paper systematically summarizes and discusses the physicochemical properties and synthesis methods of Na_(2)Ti_(3)O_(7).Then,the sodium storage mechanisms,key issues and challenges,and the optimization strategies for the electrochemical performance of Na_(2)Ti_(3)O_(7) are classified and further elaborated.Finally,remaining challenges and future research directions on the Na_(2)Ti_(3)O_(7) anode are highlighted.This review offers insights into the design of high-energy and high-safety NIBs.
基金the National Natural Science Foundation of China(Nos.51604255 and U1702251)。
文摘The low O^(2-)diffusion rate in the electro-deoxidation of titanium containing compounds by either the OS process or the FFC process leads to a low reaction speed and a low current efficiency.In this study,Ca_(3)Ti_(2)O_(7) was used as a precursor to improve the reduction speed of titanium.Because of the greater number of"diffusion channels"created in cathode as Ca^(2+) liberates from Ca_(3)Ti_(2)O_(7) precursor in the electrodeoxidation process,the O^(2-)diffusion rate was improved significantly by using Ca_(3)Ti_(2)O_(7) instead of CaTiO3 as precursor.Parallel constant voltage electrolysis(3.2 V)confirms that Ca_(3)Ti_(2)O_(7) and CaTiO3 are reduced simultaneously because of their similar crystal structures.However,the reduction area of Ca_(3)Ti_(2)O_(7) spreads much faster than that of CaTiO3,indicating a difference in the O^(2-) diffusion rate.Constant voltage cyclic voltammetry(CV)and theoretical analysis of the crystal structure were also conducted to compare the differences between Ca_(3)Ti_(2)O_(7) and CaTiO3.The results indicate that using a precursor with a greater number of soluble cations,titanium reduction speed can be greatly improved in the electro-deoxidation process.Finally,a new electrolysis method for converting and recycling excess CaO from the Ca_(3)Ti_(2)O_(7) precursor was proposed.
基金supported by the Walloon Region under the “PE PlanMarshall2.vert”program(BATWAL–1318146)。
文摘Na2Ti3O7 has attracted much attention in the field of anode materials for Na-ion batteries thanks to its non-toxicity and very low working potential of 0.3 V vs Na0/Na+.Building a clearer picture of its formation from cheap Na_(2)CO_(3) and TiO_(2) starting materials is therefore of obvious interest.Here,we report new insights from an in-situ high temperature X-ray diffraction study conducted from room temperature to 800°C,complemented by ex-situ characterizations.We were thereby able to position the previously reported Na_(4)Ti_(5)O_(12) and Na_(2)Ti_(6)O_(13) intermediate phases in a reaction scheme involving three successive steps and temperature ranges.Shifts and/or broadening of a subset of the Na_(2)Ti_(6)O_(13) reflections suggested a combination of intra-layer disorder with the well-established ordering of successive layers.This in-situ study was carried out on reproducible mixtures of Na_(2)CO_(3) and TiO_(2) in 1:3 molar ratio prepared by spraydrying of mixed aqueous suspensions.Single-phase Na_(2)Ti_(3)O_(7) was obtained after only 8 h at 800°C in air,instead of a minimum of 20 h for a conventional solid-state route using the same precursors.Microstructure analysis revealed~15 mm diameter granules made up from rectangular rods of a fewmm length presenting electrochemical properties in line with expectations.In the absence of grinding or formation of intimate composites with conductive carbon,the specific capacity of 137 m Ah/g at C/5 decreased at higher rates.
基金This work was financially supported by the Department of Science and Technology of Sichuan Province(No.2020YJ0157).
文摘A red-emitting phosphor Ca_(2.91)Si_(2)O_(7):0.09Eu^(3+) with partial Al^(3+)/P^(5+) substitution on Si^(4+) was synthesized via a simple solid-state method,and the effects of the introduction of the M^(3+/5+)(M=Al,P)ions on the crystal structure and photoluminescence performance of Ca_(2.91)Si_(2−x)M_(x)O_(7):0.09Eu^(3+) phosphors were investigated.The X-ray diffraction(XRD),energy-dispersive X-ray spectroscopy(EDS),and X-ray photoelectron spectroscopy(XPS)results revealed that the structure of Ca_(3)Si_(2)O_(7) remained the same after the introduction of Al^(3+) and P^(5+) ions.The characteristic emission of Eu^(3+)-doped Ca_(3)Si_(2−x)M_(x)O_(7) phosphors exhibited two main peaks at 617 nm(red)and 593 nm(orange)under excitation at 394 nm,which originated from the^(5)D_(0)→^(7)F_(2)and^(5)D_(0)→^(7)F_(1) electron transitions of Eu^(3+) ions.After the partial substitution of Al^(3+) and P^(5+),the red emission intensities of the Ca_(2.91)Si_(2)O_(7):0.09Eu^(3+) phosphors were significantly enhanced by 1.88-and 1.42-fold,respectively,which is attributed to the crystal-field effect around Eu^(3+).Meanwhile,the luminescence intensities of the Ca_(2.91)Si_(1.96)Al_(0.04)O_(7):0.09Eu^(3+) and Ca_(2.91)Si_(1.94)P_(0.06)O_(7):0.09Eu^(3+) phosphors at 210℃ were 79.36%and 77.53%of those at 30°C,respectively,indicating their excellent thermal stability.Moreover,the as-prepared Ca_(2.91)Si_(1.96)Al_(0.04)O_(7):0.09Eu^(3+)and Ca_(2.91)Si_(1.94)P_(0.06)O_(7):0.09Eu^(3+) red-emitting phosphors were combined with a near-ultraviolet chip of 395 nm to fabricate red-light-emitting diode(LED)and white(w)-LED devices with excellent chromaticity features.In summary,Al^(3+)/P^(5+)-substituted Ca_(2.91)Si_(2)O_(7):0.09Eu^(3+) can serve as red-emitting phosphors for applications in w-LEDs.
基金This work was partially supported by National Natural Science Foundation of China(Grant Nos.U22A20139,52102192,51772286,11974346,12074373,52072361,and 12074374)National Key R&D Program of China(Grant No.2021YFB3502701)+3 种基金Youth Innovation Promotion Association CAS(Grant No.2020222)Key Research and Development Program of Jilin Province(Grant Nos.20210201024GX,20220101208JC,and 20230101123JC)Changchun Science and Technology Planning Project(Grant No.21ZGY05)the Opening Project Key Laboratory of Transparent Opto-functional Inorganic Material,Chinese Academy of Sciences.
文摘Transparent phosphor ceramics have received increasing attention for high-brightness laser lighting,but commercially available phosphor ceramics are currently mainly limited to yellow YAG:Ce and green LuAG:Ce garnets,leaving a“cyan cavity”which is an obstacle to realizing full-color lighting.Achieving new phosphor ceramics capable of filling the cavity is a challenge.Herein,for the first time,cyan-green-emitting Ca_(3)Sc_(2)Si_(3)O_(12):Ce^(3+)(CSS:Ce)transparent ceramics have been successfully developed by two-step sintering technique under vacuum.The as-prepared CSS:Ce ceramics present high relative density of 99.7%and optical transmittance of 71%in the cyan-green spectral region.It exhibits an efficient band emission peaking at 504 nm(under 450 nm excitation)with internal/external quantum efficiency of 91%/62%.Furthermore,it has excellent thermal stability with a thermal quenching temperature(T_(0.5))of 838 K,approximately 100 K higher than that of LuAG:Ce ceramics(738 K).In addition,the CSS:Ce ceramics can withstand blue laser density of 45.6 W/mm^(2)and meanwhile generates cyan-green light with a forward luminous flux of 813 lm and forward luminous efficacy of 162 lm/W.The CSS:Ce transparent ceramics exhibit excellent luminescence performance comparable to the commercial LuAG:Ce ceramics and could be a highly promising color converter for high-brightness laser lighting.
基金financially supported by the National Natural Science Foundation of China under Grant Nos.51772266 and 51790493the National Key R&D Program of China under Grant No.2016YFA0300101.
文摘Ca_(3)Ti_(2)O_(7) with Ruddlesden-Popper structure exhibits the largest polarization among the known hybrid improper ferroelectrics.However,the high Curie temperature impedes the thorough study of phase transition through dielectric characterization.According to the previous theoretical design rule,the Curie temperature can be suppressed by increasing the tolerance factor.So,in the present work,high-quality Ca_(3-x)LaxTi_(2-x)Al_(x)O_(7)(x=0.0,0.1,0.2,0.3)ceramics with increased tolerance factors were successfully prepared.The amplitude of oxygen octahedral tilt mode indeed decreases with increasing tolerance factors,leading to a degeneration of ferroelectric polarization.However,the unexpected rigid rotation mode causes the composition-invariable coercive fields.The Curie temperatures decrease linearly with increasing x and tolerance factors.The variable-temperature dielectric constant confirms first-order improper ferroelectric transitions in Ca_(3)Ti_(2)O_(7)-based ceramics.The results of variable temperature Xray diffraction reveal the coexistence of two-phases below Curie temperature.The present work confidently confirms the first-order improper ferroelectric transition in Ca_(3)Ti_(2)O_(7)-based ceramics by combining results of variable-temperature dielectric response and in-situ X-ray powder diffraction.
