LiNi_(x)Co_(y)Al_(z)O_(2)(NCA)cathode materials are drawing widespread attention,but the huge gap between the ideal and present cyclic stability still hinders their further commercial application,especially for the Ni...LiNi_(x)Co_(y)Al_(z)O_(2)(NCA)cathode materials are drawing widespread attention,but the huge gap between the ideal and present cyclic stability still hinders their further commercial application,especially for the Ni-rich LiNi_(x)Co_(y)Al_(z)O_(2)(x>0.8,x+y+z=1)cathode material,which is owing to the structural degradation and particles'intrinsic fracture.To tackle the problems,Li_(0.5)La_(2)Al_(0.5)O_(4)in situ coated and Mn compensating doped multilayer LiNi_(0.82)Co_(0.14)Al_(0.04)O_(2)was prepared.XRD refinement indicates that La-Mn co-modifying could realize appropriate Li/Ni disorder degree.Calculated results and in situ XRD patterns reveal that the LLAO coating layer could effectively restrain crack in secondary particles benefited from the suppressed internal strain.AFM further improves as NCA-LM2 has superior mechanical property.The SEM,TEM,XPS tests indicate that the cycled cathode with LLAO-Mn modification displays a more complete morphology and less side reaction with electrolyte.DEMS was used to further investigate cathode-electrolyte interface which was reflected by gas evolution.NCA-LM2 releases less CO_(2)than NCA-P indexing on a more stable surface.The modified material presents outstanding capacity retention of 96.2%after 100 cycles in the voltage range of 3.0-4.4 V at 1C,13%higher than that of the pristine and 80.8%at 1 C after 300 cycles.This excellent electrochemical performance could be attributed to the fact that the high chemically stable coating layer of Li_(0.5)La_(2)Al_(0.5)O_(4)(LLAO)could enhance the interface and the Mn doping layer could suppress the influence of the lattice mismatch and distortion.We believe that it can be a useful strategy for the modification of Ni-rich cathode material and other advanced functional material.展开更多
High-voltage LiCoO_(2)(LCO)offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries,however,LiCoO_(2)is subject to serious structural and interfacial degradation above voltages>4.5...High-voltage LiCoO_(2)(LCO)offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries,however,LiCoO_(2)is subject to serious structural and interfacial degradation above voltages>4.55 V(vs.Li/Li^(+)).Herein,an in-situ Li_(6.25)La_(3)Zr_(2)A_(l0.25)O_(12)(LLZAO)layer is constructed on the LCO surface to achieve operating voltage at 4.6 V.The detailed characterizations(ex-situ XRD,ex-situ Raman,DFT,etc.)reveal that the LLZAO layer greatly enhances Li+conductivity attributed to the ionconducting layer on the surface/interface,and closely combines with LiCoO_(2)particle to ensure stable cathode/electrolyte interface,thus suppressing the highly reactive Co^(4+)and O^(-)triggered surface side reactions at high-voltage.Moreover,the introduction of La^(3+)/Zr^(4+)/Al^(3+)with a larger ionic radius(La^(3+)/Zr^(4+)are larger than Co^(3+))and weaker electronegativity(La/Zr/Al are weaker than Co)into Co^(3+)sites readjusts the electron cloud density between Co–O–Li,which reinforces the Co–O bond and widens the band-center gap of Co 3d and O 2p,thus restraining the detrimental phase transition(from H3 to H1-3 phase)and the formation of Co_(3)O_(4)spinel phase(attributed to lattice oxygen release),subsequently alleviating the particle cracking and structural collapse during repeated Li^(+)de/intercalation.Therefore,after 100 cycles at 3.0–4.6 V,LCO@1.0LLZAO exhibits a superior discharge capacity of 188.5 m A h g^(-1),with a capacity retention of 85.1%.The above research has brought about meaningful guidance for the evolution of cathode materials with high voltage.展开更多
Layered Ni-rich transition metal oxide is treated as the most promising alternative cathode due to their high-capacity and flexible composition.However,the severe lattice strain and slow Li-ion migration kinetics seve...Layered Ni-rich transition metal oxide is treated as the most promising alternative cathode due to their high-capacity and flexible composition.However,the severe lattice strain and slow Li-ion migration kinetics severely restrict their practical application.Herein,a novelty strategy induced pinning effect and defect structure in layered Ni-rich transition metal oxide cathodes is proposed via a facile cation(iron ion)/anion(polyanion)co-doping method.Subsequently,the effects of pinning effect and defect structure on element valence state,crystal structure,morphology,lattice strain,and electrochemical performance during lithiation/delithiation are systematically explored.The detailed characterizations(soft X-ray absorption spectroscopy(sXAS),in-situ X-ray diffraction(XRD),etc.)and density functional theory(DFT)calculation demonstrate that the pinning effects built-in LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)materials by the dual-site occupation of iron ions on lithium and transition metal sites effectively alleviate the abrupt lattice strain caused by an unfavorable phase transition and the subsequent induction of defect structures in the Li layer can greatly reduce the lithium-ion diffusion barrier.Therefore,the modified LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)exhibits a high-capacity of 206.5 mAh g^(-1)and remarkably enhanced capacity retention of 93.9%after 100 cycles,far superior to~14.1%of the pristine cathodes.Besides,an excellent discharge capacity of 180.1 mAh g^(-1)at 10 C rate is maintained,illustrating its remarkable rate capability.This work reports a pinning effect and defect engineering method to suppress the lattice strain and alleviate lithium-ion kinetic barriers in the Ni-rich layered cathodes,providing a roadmap for understanding the fundamental mechanism of an intrinsic activity modulation and structural design of layered cathode materials.展开更多
Objective:This study aimed to survey the characteristics and treatments of cancer pain in Beijing hospitals,China.Methods:At 20:00 on December 22,2009,there conducted a questionnaire survey in 2238 patients with malig...Objective:This study aimed to survey the characteristics and treatments of cancer pain in Beijing hospitals,China.Methods:At 20:00 on December 22,2009,there conducted a questionnaire survey in 2238 patients with malignant tumors of 26 hospitals in Beijing,and the survey results were statistically analyzed.Results:The 531 cases in 2238 patients had pained and 121 cases (22.79%) had outbreak pain with one week.At 20:00 on December 22,2009,199 cases (38%) in the above-mentioned 531 pain patients suffered the moderate to severe pain (pain scores ≥ 4).The number of pain (pain scores ≥ 4) patients in the consecutive three days from December 20 to December 22 were 150.Conclusion:In the 531 cancer pain patients of the surveyed hospitals,38% of the patients were not satisfied with the pain control.Doctors believed that the main reason for pain not controlled was the non-standard treatment,but patients considered to be afraid of addiction.展开更多
A 2×3 kW-level bidirectional output fiber oscillator is realized by combining the specially designed spindle-shaped ytterbium-doped fiber,non-wavelength-stabilized 976-nm LDs,and grating bandwidth optimization to...A 2×3 kW-level bidirectional output fiber oscillator is realized by combining the specially designed spindle-shaped ytterbium-doped fiber,non-wavelength-stabilized 976-nm LDs,and grating bandwidth optimization to balance transverse mode instability and stimulated Raman scattering.The maximum output powers at both ends are 3265 and 2840 W,respectively,with a total efficiency of 73.2%.The M^(2) factors of the lasers at both ends are about 1.98 and 2.38,respectively.The beam profile at both ends shows that a bidirectional output annular beam fiber oscillator has been realized,which has great potential in practical applications.展开更多
We fabricate a pair of fiber Bragg gratings(FBGs)by a visible femtosecond laser phase mask scanning technique on passive large-mode-area double-cladding fibers for multi-kilowatt fiber oscillators.The bandwidth of hig...We fabricate a pair of fiber Bragg gratings(FBGs)by a visible femtosecond laser phase mask scanning technique on passive large-mode-area double-cladding fibers for multi-kilowatt fiber oscillators.The bandwidth of high-reflection(HR)and lowreflection(LR)FBG is~1.6 nm and 0.3 nm,respectively.The reflection of the HR-FBG is higher than 99%,and that of the LR-FBG is about 10%.A bidirectional pumped all-fiber oscillator is constructed using this pair of FBGs,a record output power of 5027 W located in the signal core is achieved with a slope efficiency of~82.1%,and the beam quality factor M2is measured to be~1.6 at the maximum power.The FBGs are simply fixed on a water cooling plate without a special package,and the thermal efficiency of the HR-FBG and the LR-FBG is 2.76℃/kW and 1℃/kW,respectively.Our research provides an effective solution for robust high-power all-fiber laser oscillators.展开更多
The key to hindering the commercial application of Ni-rich layered cathode is its severe structural and interface degradation during the undesired phase transition(hexagonal to hexagonal(H2→H3)),degenerating from the...The key to hindering the commercial application of Ni-rich layered cathode is its severe structural and interface degradation during the undesired phase transition(hexagonal to hexagonal(H2→H3)),degenerating from the build-up of mechanical strain and undesired parasitic reactions.Herein,a perovskite Li_(0.35)La_(0.55)TiO_(3)(LLTO)layer is built onto Ni-rich cathodes crystal to induce layered@spinel@perovskite heterostructure to solve the root cause of capacity fade.Intensive exploration based on structure characterizations,in situ X-ray diffraction techniques,and first-principles calculations demonstrate that such a unique heterostructure not only can improve the ability of the host structure to withstand the mechanical strain but also provides fast diffusion channels for lithium ions as well as provides a protective barrier against electrolyte corrosion.Impressively,the LLTO modified LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)cathode manifests an unexpected cyclability with an extremely high-capacity retention of≈94.6%after 100 cycles,which is superior to the pristine LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)(79.8%).Furthermore,this modified electrode also shows significantly enhanced cycling stability even withstanding a high cut-off voltage of 4.6 V.This surface self-reconstruction strategy provides deep insight into the structure/interface engineering to synergistically stabilize structure stability and regulate the physicochemical properties of Ni-rich cathodes,which will also unlock a new perspective of surface interface engineering for layered cathode materials.展开更多
The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years.However, stimulated Raman scattering(SRS) is still a major factor limiting the further power scaling. Here,...The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years.However, stimulated Raman scattering(SRS) is still a major factor limiting the further power scaling. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating(CTFBG) for the first time. The CTFBG is designed and inscribed in large-mode-area(LMA) fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG inserted between the seed laser and the amplifier stage, an SRS suppression ratio of ~10 dB is achieved in spectrum at the maximum output laser power of 2.35 kW,and there is no reduction in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.展开更多
Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a c...Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.展开更多
Fibre lasers operating at the mid-IR have attracted enormous interest due to the plethora of applications in defence,security,medicine,and so on.However,no continuous-wave(CW)fibre lasers beyond 4μm based on rare-ear...Fibre lasers operating at the mid-IR have attracted enormous interest due to the plethora of applications in defence,security,medicine,and so on.However,no continuous-wave(CW)fibre lasers beyond 4μm based on rare-earth-doped fibres have been demonstrated thus far.Here,we report efficient mid-IR laser emission from HBr-filled silica hollow-core fibres(HCFs)for the first time.By pumping with a self-developed thulium-doped fibre amplifier seeded by several diode lasers over the range of 1940–1983 nm,narrow linewidth mid-IR emission from 3810 to 4496 nm has been achieved with a maximum laser power of about 500 mW and a slope efficiency of approximately 18%.To the best of our knowledge,the wavelength of 4496 nm with strong absorption in silica-based fibres is the longest emission wavelength from a CW fibre laser,and the span of 686 nm is also the largest tuning range achieved to date for any CW fibre laser.By further reducing the HCF transmission loss,increasing the pump power,improving the coupling efficiency,and optimizing the fibre length together with the pressure,the laser efficiency and output power are expected to increase significantly.This work opens new opportunities for broadly tunable high-power mid-IR fibre lasers,especially beyond 4μm.展开更多
We report here an ultra-broadband linearly polarized(LP)LP01-LP11 mode converter operating at 1μm based on a long period fiber grating(LPFG)fabricated in a conventional two-mode fiber(TMF)by a line-focused CO2 laser....We report here an ultra-broadband linearly polarized(LP)LP01-LP11 mode converter operating at 1μm based on a long period fiber grating(LPFG)fabricated in a conventional two-mode fiber(TMF)by a line-focused CO2 laser.The measured 3d B bandwidth is about 240 nm,which is the broadest bandwidth for such fiber mode converters.The maximum conversion efficiency between the LP01 and LP11 modes is>99%over the range of 1000 nm to 1085 nm,almost covering the whole emission band of Yb3+,which is useful for further power scaling of high-power fiber lasers operating at the 1μm band.展开更多
We found the beam quality factor M^(2)of the fundamental mode as a function of wavelength is U-shaped in the working photonic bandgap(PBG) of an all-solid PBG fiber(AS-PBGF) for the first time,to the best of our knowl...We found the beam quality factor M^(2)of the fundamental mode as a function of wavelength is U-shaped in the working photonic bandgap(PBG) of an all-solid PBG fiber(AS-PBGF) for the first time,to the best of our knowledge,and our simulation results also match well with the phenomenon.The normal band that is near the high-frequency edge of the third PBG integrates the lowest M^(2)and single-mode operation simultaneously,while the other two edge regions suffer from anomalous variation of M^(2)versus wavelength.The general applicability of this finding can be further extended to other PBGs and also other representative structures in the AS-PBGF field.展开更多
基金supported in part by the High Performance Computing Center of Central South Universitythe financial support from the Government of Chongzuo,Guangxi Zhuang Autonomous Region(Fund No.FA2020011FA20210713)
文摘LiNi_(x)Co_(y)Al_(z)O_(2)(NCA)cathode materials are drawing widespread attention,but the huge gap between the ideal and present cyclic stability still hinders their further commercial application,especially for the Ni-rich LiNi_(x)Co_(y)Al_(z)O_(2)(x>0.8,x+y+z=1)cathode material,which is owing to the structural degradation and particles'intrinsic fracture.To tackle the problems,Li_(0.5)La_(2)Al_(0.5)O_(4)in situ coated and Mn compensating doped multilayer LiNi_(0.82)Co_(0.14)Al_(0.04)O_(2)was prepared.XRD refinement indicates that La-Mn co-modifying could realize appropriate Li/Ni disorder degree.Calculated results and in situ XRD patterns reveal that the LLAO coating layer could effectively restrain crack in secondary particles benefited from the suppressed internal strain.AFM further improves as NCA-LM2 has superior mechanical property.The SEM,TEM,XPS tests indicate that the cycled cathode with LLAO-Mn modification displays a more complete morphology and less side reaction with electrolyte.DEMS was used to further investigate cathode-electrolyte interface which was reflected by gas evolution.NCA-LM2 releases less CO_(2)than NCA-P indexing on a more stable surface.The modified material presents outstanding capacity retention of 96.2%after 100 cycles in the voltage range of 3.0-4.4 V at 1C,13%higher than that of the pristine and 80.8%at 1 C after 300 cycles.This excellent electrochemical performance could be attributed to the fact that the high chemically stable coating layer of Li_(0.5)La_(2)Al_(0.5)O_(4)(LLAO)could enhance the interface and the Mn doping layer could suppress the influence of the lattice mismatch and distortion.We believe that it can be a useful strategy for the modification of Ni-rich cathode material and other advanced functional material.
基金supported by the Chongzuo Science and Technology Program Project Fund(No.FA20210713)。
文摘High-voltage LiCoO_(2)(LCO)offers a prelude to breaking the bottleneck of the energy density of lithium-ion batteries,however,LiCoO_(2)is subject to serious structural and interfacial degradation above voltages>4.55 V(vs.Li/Li^(+)).Herein,an in-situ Li_(6.25)La_(3)Zr_(2)A_(l0.25)O_(12)(LLZAO)layer is constructed on the LCO surface to achieve operating voltage at 4.6 V.The detailed characterizations(ex-situ XRD,ex-situ Raman,DFT,etc.)reveal that the LLZAO layer greatly enhances Li+conductivity attributed to the ionconducting layer on the surface/interface,and closely combines with LiCoO_(2)particle to ensure stable cathode/electrolyte interface,thus suppressing the highly reactive Co^(4+)and O^(-)triggered surface side reactions at high-voltage.Moreover,the introduction of La^(3+)/Zr^(4+)/Al^(3+)with a larger ionic radius(La^(3+)/Zr^(4+)are larger than Co^(3+))and weaker electronegativity(La/Zr/Al are weaker than Co)into Co^(3+)sites readjusts the electron cloud density between Co–O–Li,which reinforces the Co–O bond and widens the band-center gap of Co 3d and O 2p,thus restraining the detrimental phase transition(from H3 to H1-3 phase)and the formation of Co_(3)O_(4)spinel phase(attributed to lattice oxygen release),subsequently alleviating the particle cracking and structural collapse during repeated Li^(+)de/intercalation.Therefore,after 100 cycles at 3.0–4.6 V,LCO@1.0LLZAO exhibits a superior discharge capacity of 188.5 m A h g^(-1),with a capacity retention of 85.1%.The above research has brought about meaningful guidance for the evolution of cathode materials with high voltage.
基金financially supported by the Science and Technology of Guangxi Zhuang Autonomous Region(the Guangxi special Fund for Scientific Center and Talent Resources:AD18281073,Chongke 2018AD15002 and FA2020011)。
文摘Layered Ni-rich transition metal oxide is treated as the most promising alternative cathode due to their high-capacity and flexible composition.However,the severe lattice strain and slow Li-ion migration kinetics severely restrict their practical application.Herein,a novelty strategy induced pinning effect and defect structure in layered Ni-rich transition metal oxide cathodes is proposed via a facile cation(iron ion)/anion(polyanion)co-doping method.Subsequently,the effects of pinning effect and defect structure on element valence state,crystal structure,morphology,lattice strain,and electrochemical performance during lithiation/delithiation are systematically explored.The detailed characterizations(soft X-ray absorption spectroscopy(sXAS),in-situ X-ray diffraction(XRD),etc.)and density functional theory(DFT)calculation demonstrate that the pinning effects built-in LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)materials by the dual-site occupation of iron ions on lithium and transition metal sites effectively alleviate the abrupt lattice strain caused by an unfavorable phase transition and the subsequent induction of defect structures in the Li layer can greatly reduce the lithium-ion diffusion barrier.Therefore,the modified LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)exhibits a high-capacity of 206.5 mAh g^(-1)and remarkably enhanced capacity retention of 93.9%after 100 cycles,far superior to~14.1%of the pristine cathodes.Besides,an excellent discharge capacity of 180.1 mAh g^(-1)at 10 C rate is maintained,illustrating its remarkable rate capability.This work reports a pinning effect and defect engineering method to suppress the lattice strain and alleviate lithium-ion kinetic barriers in the Ni-rich layered cathodes,providing a roadmap for understanding the fundamental mechanism of an intrinsic activity modulation and structural design of layered cathode materials.
文摘Objective:This study aimed to survey the characteristics and treatments of cancer pain in Beijing hospitals,China.Methods:At 20:00 on December 22,2009,there conducted a questionnaire survey in 2238 patients with malignant tumors of 26 hospitals in Beijing,and the survey results were statistically analyzed.Results:The 531 cases in 2238 patients had pained and 121 cases (22.79%) had outbreak pain with one week.At 20:00 on December 22,2009,199 cases (38%) in the above-mentioned 531 pain patients suffered the moderate to severe pain (pain scores ≥ 4).The number of pain (pain scores ≥ 4) patients in the consecutive three days from December 20 to December 22 were 150.Conclusion:In the 531 cancer pain patients of the surveyed hospitals,38% of the patients were not satisfied with the pain control.Doctors believed that the main reason for pain not controlled was the non-standard treatment,but patients considered to be afraid of addiction.
基金supported by the Funding for Distinguished Yong Scholars of Hunan Province(No.2023JJ10057)the Training Program for Excellent Young Innovations of Changsha(No.kq2305038)the Basic Scientific Research Program(No.JCKY2021525B015).
文摘A 2×3 kW-level bidirectional output fiber oscillator is realized by combining the specially designed spindle-shaped ytterbium-doped fiber,non-wavelength-stabilized 976-nm LDs,and grating bandwidth optimization to balance transverse mode instability and stimulated Raman scattering.The maximum output powers at both ends are 3265 and 2840 W,respectively,with a total efficiency of 73.2%.The M^(2) factors of the lasers at both ends are about 1.98 and 2.38,respectively.The beam profile at both ends shows that a bidirectional output annular beam fiber oscillator has been realized,which has great potential in practical applications.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.11974427 and 12004431)State Key Laboratory of Pulsed Power Laser(Nos.SKL-2020ZR05 and SKL2021ZR01)Postgraduate Scientific Research Innovation Project of Hunan Province(No.CX20200046)。
文摘We fabricate a pair of fiber Bragg gratings(FBGs)by a visible femtosecond laser phase mask scanning technique on passive large-mode-area double-cladding fibers for multi-kilowatt fiber oscillators.The bandwidth of high-reflection(HR)and lowreflection(LR)FBG is~1.6 nm and 0.3 nm,respectively.The reflection of the HR-FBG is higher than 99%,and that of the LR-FBG is about 10%.A bidirectional pumped all-fiber oscillator is constructed using this pair of FBGs,a record output power of 5027 W located in the signal core is achieved with a slope efficiency of~82.1%,and the beam quality factor M2is measured to be~1.6 at the maximum power.The FBGs are simply fixed on a water cooling plate without a special package,and the thermal efficiency of the HR-FBG and the LR-FBG is 2.76℃/kW and 1℃/kW,respectively.Our research provides an effective solution for robust high-power all-fiber laser oscillators.
基金supported by the Science and Technology of Guangxi Zhuang Autonomous Region(Gangxi Special Fund for Scientific Center and Talent Resources,Nos.FA2020011 and FA20210713).
文摘The key to hindering the commercial application of Ni-rich layered cathode is its severe structural and interface degradation during the undesired phase transition(hexagonal to hexagonal(H2→H3)),degenerating from the build-up of mechanical strain and undesired parasitic reactions.Herein,a perovskite Li_(0.35)La_(0.55)TiO_(3)(LLTO)layer is built onto Ni-rich cathodes crystal to induce layered@spinel@perovskite heterostructure to solve the root cause of capacity fade.Intensive exploration based on structure characterizations,in situ X-ray diffraction techniques,and first-principles calculations demonstrate that such a unique heterostructure not only can improve the ability of the host structure to withstand the mechanical strain but also provides fast diffusion channels for lithium ions as well as provides a protective barrier against electrolyte corrosion.Impressively,the LLTO modified LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)cathode manifests an unexpected cyclability with an extremely high-capacity retention of≈94.6%after 100 cycles,which is superior to the pristine LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)(79.8%).Furthermore,this modified electrode also shows significantly enhanced cycling stability even withstanding a high cut-off voltage of 4.6 V.This surface self-reconstruction strategy provides deep insight into the structure/interface engineering to synergistically stabilize structure stability and regulate the physicochemical properties of Ni-rich cathodes,which will also unlock a new perspective of surface interface engineering for layered cathode materials.
基金supported by the National Natural Science Foundation of China(No.11274385)
文摘The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years.However, stimulated Raman scattering(SRS) is still a major factor limiting the further power scaling. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating(CTFBG) for the first time. The CTFBG is designed and inscribed in large-mode-area(LMA) fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG inserted between the seed laser and the amplifier stage, an SRS suppression ratio of ~10 dB is achieved in spectrum at the maximum output laser power of 2.35 kW,and there is no reduction in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.
基金the National Natural Science Foundation of China(Nos.61735007 and 61705266).
文摘Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.
基金the Outstanding Youth Science Fund Project of Hunan Province Natural Science Foundation(2019JJ20023)National Natural Science Foundation of China(NSFC)(11974427,12004431)+1 种基金State Key Laboratory of Pulsed Power Laser Technology(SKL-2020-ZR05,SKL-2021-ZR01)Postgraduate Scientific Research Innovation Project of Hunan Province(CX20190026,CX20200047).
文摘Fibre lasers operating at the mid-IR have attracted enormous interest due to the plethora of applications in defence,security,medicine,and so on.However,no continuous-wave(CW)fibre lasers beyond 4μm based on rare-earth-doped fibres have been demonstrated thus far.Here,we report efficient mid-IR laser emission from HBr-filled silica hollow-core fibres(HCFs)for the first time.By pumping with a self-developed thulium-doped fibre amplifier seeded by several diode lasers over the range of 1940–1983 nm,narrow linewidth mid-IR emission from 3810 to 4496 nm has been achieved with a maximum laser power of about 500 mW and a slope efficiency of approximately 18%.To the best of our knowledge,the wavelength of 4496 nm with strong absorption in silica-based fibres is the longest emission wavelength from a CW fibre laser,and the span of 686 nm is also the largest tuning range achieved to date for any CW fibre laser.By further reducing the HCF transmission loss,increasing the pump power,improving the coupling efficiency,and optimizing the fibre length together with the pressure,the laser efficiency and output power are expected to increase significantly.This work opens new opportunities for broadly tunable high-power mid-IR fibre lasers,especially beyond 4μm.
基金supported by the Outstanding Youth Science Fund of Natural Science Foundation of Hunan Province(No.2019JJ20023)the National Natural Science Foundation of China(No.11974427)
文摘We report here an ultra-broadband linearly polarized(LP)LP01-LP11 mode converter operating at 1μm based on a long period fiber grating(LPFG)fabricated in a conventional two-mode fiber(TMF)by a line-focused CO2 laser.The measured 3d B bandwidth is about 240 nm,which is the broadest bandwidth for such fiber mode converters.The maximum conversion efficiency between the LP01 and LP11 modes is>99%over the range of 1000 nm to 1085 nm,almost covering the whole emission band of Yb3+,which is useful for further power scaling of high-power fiber lasers operating at the 1μm band.
基金financially supported by the National Natural Science Foundation of China (Nos. 62035015 and 61805280)the Innovation Group of Hunan Province, China (No. 2019JJ10005)+1 种基金the Research Plan of National University of Defense Technology (No. ZK19-07)the Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology (No. SKL2020ZR07)
文摘We found the beam quality factor M^(2)of the fundamental mode as a function of wavelength is U-shaped in the working photonic bandgap(PBG) of an all-solid PBG fiber(AS-PBGF) for the first time,to the best of our knowledge,and our simulation results also match well with the phenomenon.The normal band that is near the high-frequency edge of the third PBG integrates the lowest M^(2)and single-mode operation simultaneously,while the other two edge regions suffer from anomalous variation of M^(2)versus wavelength.The general applicability of this finding can be further extended to other PBGs and also other representative structures in the AS-PBGF field.