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 ca...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.展开更多
Li-rich oxides are considered as the most commercial potential cathode materials due to the high theoretical specific discharge capacity. Here, ZrO_(2) in different crystalline states are applied as the coating layers...Li-rich oxides are considered as the most commercial potential cathode materials due to the high theoretical specific discharge capacity. Here, ZrO_(2) in different crystalline states are applied as the coating layers to enhance the electrochemical performance of hollow Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_(2) materials.Meanwhile, a series of characterizations(XRD, SEM, TEM, EDX etc.) are conducted to compare the effects of ZrO_(2) coating layer with different crystalline states on the host material. The results elucidate that the Li-rich Mn-based material with the polycrystal ZrO_(2) coating layer has a slight advantage in rate performance, while the host material with the single crystal ZrO_(2)-coating layer has a better cycling performance and effectively suppresses voltage decay with the effect of excellently inhibiting layered to spinel-like phase transition and metal dissolution during charging and discharging process.展开更多
The P2-type manganese-based Na_(0.7)MnO_(2) cathode materials attract great interest due to their high theoretical capacity.However,these materials suffer from rapid capacity fading,poor rate performance and severe vo...The P2-type manganese-based Na_(0.7)MnO_(2) cathode materials attract great interest due to their high theoretical capacity.However,these materials suffer from rapid capacity fading,poor rate performance and severe voltage decay resulting from phase transition and sluggish reaction kinetics.In this work we report a novel Nb-doped Na_(0.7)[Ni_(0.3)Co_(0.1)Mn_(0.6)]_(1-x)Nb_(x)O_(2) with significantly suppre ssed voltage decay and enhanced cycling stability.The strong Nb-O bond can efficiently stabilize the TMO fra mework,and the as prepared material demonstrates much lower discharge midpoint voltage decay(0.132 V) than that of pristine one(0.319 V) after 200 cycles.Consequently,a remarkably improved cycling perfo rmance with a capacity retention of 87.9% after 200 cycle at 0.5 C is achieved,showing a 2.4 fold improvement as compared to the control sample Na_(0.7)Ni_(0.3)Co_(0.1)Mn_(0.6)O_(2)(~37% rotation).Even at 2 C,a capacity retention of 68.4% is retained after 500 cycles.Remarkably,the as prepared material can be applied at low temperature of-20℃,showing a capacity retention of 81% as compared to that at room temperature.展开更多
The voltage decay of lithium-rich layered oxides(LLOs)is still one of the key challenges for their application in commercial battery although these materials possess the advantages of high specific capacity and low co...The voltage decay of lithium-rich layered oxides(LLOs)is still one of the key challenges for their application in commercial battery although these materials possess the advantages of high specific capacity and low cost.In this work,the relationship between voltage decay and tap density of LLOs has been focused.The voltage decay can be significantly suppressed with the increasing tap density as well as the homogenization of the primary or secondary particle size of agglomerated spherical LLOs.Experimental results have shown that an extreme small voltage decay of 0.98 m V cycle^(-1)can be obtained through adjusting the tap density of agglomerated spherical LLOs to 1.99 g cm^(-3),in which the size of primary and secondary particles are uniform.Our work offers a new insight towards the voltage decay and capacity fading of LLOs through precursor preparation process,promoting their application in the real battery in the future.展开更多
Li-rich layered oxide(LRLO)cathodes have been regarded as promising candidates for next-generation Li-ion batteries due to their exceptionally high energy density,which combines cationic and anionic redox activities.H...Li-rich layered oxide(LRLO)cathodes have been regarded as promising candidates for next-generation Li-ion batteries due to their exceptionally high energy density,which combines cationic and anionic redox activities.However,continuous voltage decay during cycling remains the primary obstacle for practical applications,which has yet to be fundamentally addressed.It is widely acknowledged that voltage decay originates from the irreversible migration of transition metal ions,which usually further exacerbates structural evolution and aggravates the irreversible oxygen redox reactions.Recently,constructing O2-type structure has been considered one of the most promising approaches for inhibiting voltage decay.In this review,the relationship between voltage decay and structural evolution is systematically elucidated.Strategies to suppress voltage decay are systematically summarized.Additionally,the design of O2-type structure and the corresponding mechanism of suppressing voltage decay are comprehensively discussed.Unfortunately,the reported O2-type LRLO cathodes still exhibit partially disordered structure with extended cycles.Herein,the factors that may cause the irreversible transition metal migrations in O2-type LRLO materials are also explored,while the perspectives and challenges for designing high-performance O2-type LRLO cathodes without voltage decay are proposed.展开更多
<span style="font-family:Verdana;">This manuscript presents a simple method for excess minority carriers’ lifetime measurement</span><span style="font-family:""> </span&g...<span style="font-family:Verdana;">This manuscript presents a simple method for excess minority carriers’ lifetime measurement</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">within the base region of p-n junction polycrystalline solar </span><span style="font-family:Verdana;">cell</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">in transient mode.</span><span style="font-family:""> </span><span style="font-family:Verdana;">This work is an experimental transient</span><span style="font-family:Verdana;"> 3-Dimensionnal study.</span><span style="font-family:""> </span><span style="font-family:Verdana;">The magnitude of the magnetic field B is varied from 0 mT to 0.045 mT. Indeed, the solar cell is illuminated by a stroboscopic flash with air mass 1.5</span><span style="font-family:""> </span><span style="font-family:Verdana;">and under magnetic field in transient state.</span><span style="font-family:""> </span><span style="font-family:Verdana;">The experimental details are assumed in a figure. The procedure is outlined by the Open Circuit Voltage Decay analysis. Effective minority carrier life-time is calculated by fitting the linear zone of the transient voltage decay curve</span><span style="font-family:""> </span><span style="font-family:Verdana;">because linear decay is an ideal decay. The kaleidagraph software permits access to the slope of the curve which is inversely proportional to the</span><span style="font-family:""> </span><span style="font-family:Verdana;">lifetime. The external magnetic effects</span><span style="font-family:""> </span><span style="font-family:Verdana;">on minority carriers’ effective lifetime </span><span style="font-family:Verdana;">is</span><span style="font-family:Verdana;"> then</span><span style="font-family:""> </span><span style="font-family:Verdana;">presented and analyzed.</span><span style="font-family:""> </span><span style="font-family:Verdana;">The analysis show</span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;"> that the charge carrier</span><span style="font-family:Verdana;">’</span><span style="font-family:Verdana;">s effective lifetime decrease with the magnetic field increase.</span>展开更多
Lithium-rich layered oxides(LLOs)have been extensively studied as cathode materials for lithium-ion batteries(LIBs)by researchers all over the world in the past decades due to their high specific capacities and high c...Lithium-rich layered oxides(LLOs)have been extensively studied as cathode materials for lithium-ion batteries(LIBs)by researchers all over the world in the past decades due to their high specific capacities and high charge-discharge voltages.However,as cathode materials LLOs have disadvantages of significant voltage and capacity decays during the charge-discharge cycling.It was shown in the past that fine-tuning of structures and compositions was critical to the performances of this kind of materials.In this report,LLOs with target composition of Li1.17Mn0.50Ni0.24Co0.09O2 were prepared by carbonate co-precipitation method with different pH values.X-ray powder diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscope(TEM),and electrochemical impedance spectroscopies(EIS)were used to investigate the structures and morphologies of the materials and to understand the improvements of their electrochemical performances.With the pH values increased from 7.5 to 8.5,the Li/Ni ratios in the compositions decreased from 5.17 to 4.64,and the initial Coulombic efficiency,cycling stability and average discharge voltages were gained impressively.Especially,the material synthesized at pH=8.5 delivered a reversible discharge capacity of 263 mAhg−1 during the first cycle,with 79.0%initial Coulombic efficiency,at the rate of 0.1 C and a superior capacity retention of 94%after 100 cycles at the rate of 1 C.Furthermore,this material exhibited an initial average discharge voltage of 3.65 V,with a voltage decay of only 0.09 V after 50 charge-discharge cycles.The improved electrochemical performances by varying the pH values in the synthesis process can be explained by the mitigation of layered-to-spinel phase transformation and the reduction of solid-electrolyte interface(SEI)resistance.We hope this work can shed some light on the alleviation of voltage and capacity decay issues of the LLOs cathode materials.展开更多
Minority carrier lifetimesτare a fundamental parameter in semiconductor devices,representing the average time it takes for excess minority carriers to recombine.This characteristic is crucial for understanding and op...Minority carrier lifetimesτare a fundamental parameter in semiconductor devices,representing the average time it takes for excess minority carriers to recombine.This characteristic is crucial for understanding and optimizing the performance of semiconductor materials,as it directly influences charge carrier dynamics and overall device efficiency.This work presents a development of PbS thin film deposited by thermal evaporation,at which the PbS thin film was further employed for structural,optical properties,andτ.Especially,the PbS film is probed with an in-house setup for identifying theτ.The procedure is to subject the PbS thin film with a flashlight from a light source with a middle rotating frequency.The derivedτin the in-house characterization setup agrees well with the value from the higher cost characterizing approach of photoluminescence.Therefore,the in-house setup provides additional tools for identifying theτvalues for semiconductor devices.展开更多
The utilization of Li-rich layered oxides(LLOs)as cathodes in high-energy Li-ion batteries is significantly hindered by serious voltage decay and capacity fading due to irreversible oxygen release and transition metal...The utilization of Li-rich layered oxides(LLOs)as cathodes in high-energy Li-ion batteries is significantly hindered by serious voltage decay and capacity fading due to irreversible oxygen release and transition metal(TM)migration triggered by the lattice strain.Herein,B ions are effectively incorporated into the tetrahedral vacancies situated between TM slab and Li layer of LLOs.The robust B-O bond,along with the low Bader charge of oxygen within BO_(4) tetrahedra,alleviates excessive oxidation of O anions while substantially reinforcing the oxygen framework.Consequently,the B-doped LLO sample exhibits only slight variation in lattice parameters,especially the c-axis,which can be characterized as exhibiting“zero-strain”as supported by in situ XRD data.As a result,the discharge capacity of the B-LLO sample maintains 210.66 mAh·g^(−1) after 300 cycles,with a retention ratio of 90.7%.展开更多
Li-rich layered oxides have become one of the most concerned cathode materials for high-energy lithiumion batteries, but they still suffer from poor cycling stability and detrimental voltage decay, especially at eleva...Li-rich layered oxides have become one of the most concerned cathode materials for high-energy lithiumion batteries, but they still suffer from poor cycling stability and detrimental voltage decay, especially at elevated temperature. Herein, we proposed a surface heterophase coating engineering based on amorphous/crystalline Li3 PO4 to address these issues for Li-rich layered oxides via a facile wet chemical method. The heterophase coating layer combines the advantages of physical barrier effect achieved by amorphous Li3 PO4 with facilitated Li+diffusion stemmed from crystalline Li3 PO4. Consequently, the modified Li(1.2) Ni(0.2) Mn(0.6) O2 delivers higher initial coulombic efficiency of 92% with enhanced cycling stability at 55 °C(192.9 mAh/g after 100 cycles at 1 C). More importantly, the intrinsic voltage decay has been inhibited as well, i.e. the average potential drop per cycle decreases from 5.96 mV to 2.99 mV. This surface heterophase coating engineering provides an effective strategy to enhance the high-temperature electrochemical performances of Li-rich layered oxides and guides the direction of surface modification strategies for cathode materials in the future.展开更多
Lithium-rich manganese-based oxides(LRMOs)have been considered as one of the most promising cathode materials owing to their superior specific capacity and high operating voltage.However,their largescale commercial ap...Lithium-rich manganese-based oxides(LRMOs)have been considered as one of the most promising cathode materials owing to their superior specific capacity and high operating voltage.However,their largescale commercial applications are limited due to problems such as structural instability,voltage decay,and poor cycle stability.Herein,pre-generated oxygen vacancies and oxygen-deficient phase were introduced to Li_(1.2)Mn_(0.6)Ni_(0.2)O_(2)(LMNO)using a facile urea-assisted mixed gas treatment(UMGT)method for facilitating electronic and ionic conductivity,reducing the surface oxygen partial pressure,and suppressing the release of lattice oxygen.Compared with the pristine LMNO material,the UMGT sample modified at 200℃exhibited enhanced discharge capacity,capacity retention,and rate capability.In addition,the Li+diffusion coefficient significantly improved by 50%than that of the reference LMNO.More importantly,the voltage decay was effectively suppressed,with average potential decreasing from 0.53 V(LMNO)to 0.39 V(UMGT-200)after 200 cycles at 1 C.The proposed UMGT method provides an effective strategy to alleviate the phase transition and improve the electrochemical performance for lithium-rich materials,and identifies a promising research direction to inhibit the voltage decay of layered anion redox cathode materials.展开更多
The emergence of anionic redox reactions in layered transition metal oxide cathodes provides practical opportunity to boost the energy density of rechargeable batteries.However,the activation of anionic redox reaction...The emergence of anionic redox reactions in layered transition metal oxide cathodes provides practical opportunity to boost the energy density of rechargeable batteries.However,the activation of anionic redox reaction in layered oxides has significant voltage hysteresis and decay that reduce battery performance and limit commercialization.Here,we critically review the up-todate development of anionic redox reaction in layered oxide cathodes,summarize the proposed reaction mechanism,and unveil their connection to voltage hysteresis and decay based on the state-of-the-art progress.In addition,advances associated with various modification approaches to mitigate the voltage hysteresis/decay in layered transition metal oxide cathodes are also included.Finally,we conclude with an appraisal of further research directions including rational design of high-performance layered oxide cathodes with reversible anionic redox reactions and suppressed voltage hysteresis/decay.Findings will be of immediate benefit to the development of layered oxide cathodes for high performance rechargeable batteries.展开更多
Migration of transition metal(TM)ions out of the TM layer is detrimental and unavoidable in lithium-rich layered oxides,which drives in-plane cation migration,O_(2)release and energy loss.Since out-of-plane migration ...Migration of transition metal(TM)ions out of the TM layer is detrimental and unavoidable in lithium-rich layered oxides,which drives in-plane cation migration,O_(2)release and energy loss.Since out-of-plane migration generally occurs through tetrahedral interstices(TLi)in the Li layer,doping TLi sites has been believed as a promising way to block migration pathways at the dopant site.However,with only trace dopants(<1at.%)sparsely distributed in bulk,the ability of isolated dopants to suppress cation disorder in undoped regions remains unknown—largely due to no suitable model materials.Here,combining atomic-scale imaging,X-ray diffraction measurements and first-principles calculations,we demonstrate that W6+ions(0.75at.%)can occupy TLi sites in Li_(1.2)Mn_(0.6)Ni_(0.2)O_(2).TLi-site doping maximizes dopant efficiency,as each single W^(6+)ion exerts a long-range Coulomb repulsion on TM/Li^(+)ions in the TM layer,suppressing both in-plane and out-of-plane cation migration over a broad range(∼2nm diameter),in contrast to local stabilization via other doping techniques.Remarkably,cation ordering is preserved for over 250 cycles,far exceeding the limited structural stability(∼50 cycles)typically achieved with conventional modification strategies.Consequently,O2 release and formation of low-voltage Mn^(3+)/Mn^(4+)redox couple are inhibited,resulting in negligible voltage decay.展开更多
With the rapid development of the economy,increasing demand for energy storage and electric vehicles require electrode materials for batteries with high energy density,safety,and cyclability,especially for lithium-ion...With the rapid development of the economy,increasing demand for energy storage and electric vehicles require electrode materials for batteries with high energy density,safety,and cyclability,especially for lithium-ion(Li-ion)battery cathodes.However,the understanding of their degradation mechanism remains insufficient due to the complex battery system,the transient nature of the de/lithiation processes,and the lack of advanced characterization techniques.Among these challenges,the mechanism of the Li-rich layered cathode family with high operating voltage and cationic-anionic hybrid charge compensation is particularly difficult to study.For the Li-rich family,their electrochemical mechanisms,for example,oxygen redox reaction and structural evolution,were almost impossible to completely clarify in terms of conventional characterization techniques until the development of various in situ techniques.It is obvious that advanced in situ techniques have accelerated the pace of scientific truth exploration.In this review,these intricate mechanisms revealed by various in situ techniques are summarized to clarify the failure mechanism of Li-rich layered cathodes,and an outlook on the application of these advanced techniques within different battery systems is provided.This review highlights how in situ devices can clearly reveal complex mechanisms and further provides the consultation on characterization techniques for mechanism exploration in various research fields.展开更多
Coupled with anionic and cationic redox chemistry,Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries.However,irreversible lattice oxygen loss would...Coupled with anionic and cationic redox chemistry,Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries.However,irreversible lattice oxygen loss would exacerbate irreversible transition metal migration,resulting in a drastic voltage decay and capacity degeneration.Herein,a metastable layered Li-excess cathode material,T2-type Li_(0.72)[Li_(0.12)Ni_(0.36)Mn_(0.52)]O_(2),was developed,in which both oxygen stacking arrangement and Li coordination environment fundamentally differ from that in conventional O3-type layered structures.By means of the reversible Li migration processes and structural evolutions,not only can voltage decay be effectively restrained,but also excellent capacity retention can be achieved upon long-term cycling.Moreover,irreversible/reversible anionic/cationic redox activities have been well assigned and quantified by various in/ex-situ spectroscopic techniques,further clarifying the charge compensation mechanism associated with(de)lithiation.These findings of the novel T2 structure with the enhanced anionic redox stability will provide a new scope for the development of high-energy-density Li-rich cathode materials.展开更多
High-capacity Li-rich cathode materials can significantly improve the energy density of lithium-ion batteries, which is the key limitation to miniaturization of electronic devices and further improvement of electrical...High-capacity Li-rich cathode materials can significantly improve the energy density of lithium-ion batteries, which is the key limitation to miniaturization of electronic devices and further improvement of electrical-vehicle mileage. However, severe voltage decay hinders the further commercialization of these materials. Insights into the relationship between the inherent structural stability and external appearance of the voltage decay in high-energy Li-rich cathode materials are critical to solve this problem. Here, we demonstrate that structural evolution can be significantly inhibited by the intentional introduction of certain adventive cations （such as Ni2~） or by premeditated reservation of some of the original Li~ ions in the Li slab in the delithiated state. The voltage decay of Li-rich cathode materials over 100 cycles decreased from 500 to 90 or 40 mV upon introducing Ni2~ or retaining some Li~ ions in the Li slab, respectively. The cations in the Li slab can serve as stabilizers to reduce the repulsion between the two neighboring oxygen layers, leading to improved thermodynamic stability. Meanwhile, the cations also suppress transition metal ion migration into the Li slab, thereby inhibiting structural evolution and mitigating voltage decay. These findings provide insights into the origin of voltage decay in Li-rich cathode materials and set new guidelines for designing these materials for high-energy-density Li-ion batteries.展开更多
基金supported by the 21C Innovation Laboratory,Contemporary Amperex Technology Ltd. by project No. 21C-OP-202103the National Natural Science Foundation of China(52072061)。
文摘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.
基金supported by the National Natural Science Foundation of China (No. 51604081 and 51974368)the Fundamental Research Funds for the Central Universities of Central South University (No. 2019zzts942)。
文摘Li-rich oxides are considered as the most commercial potential cathode materials due to the high theoretical specific discharge capacity. Here, ZrO_(2) in different crystalline states are applied as the coating layers to enhance the electrochemical performance of hollow Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_(2) materials.Meanwhile, a series of characterizations(XRD, SEM, TEM, EDX etc.) are conducted to compare the effects of ZrO_(2) coating layer with different crystalline states on the host material. The results elucidate that the Li-rich Mn-based material with the polycrystal ZrO_(2) coating layer has a slight advantage in rate performance, while the host material with the single crystal ZrO_(2)-coating layer has a better cycling performance and effectively suppresses voltage decay with the effect of excellently inhibiting layered to spinel-like phase transition and metal dissolution during charging and discharging process.
基金the financial supports from the National Natural Science Foundation of China (No.51774251)Hebei Natural Science Foundation for Distinguished Young Scholars (No.B2017203313)+2 种基金Hundred Excellent Innovative Talents Support Program in Hebei Province (No.SLRC2017057)Talent Engineering Training Funds of Hebei Province (No.A201802001)the Opening Project of the State Key Laboratory of Advanced Chemical Power Sources (No. SKL-ACPS-C-11)。
文摘The P2-type manganese-based Na_(0.7)MnO_(2) cathode materials attract great interest due to their high theoretical capacity.However,these materials suffer from rapid capacity fading,poor rate performance and severe voltage decay resulting from phase transition and sluggish reaction kinetics.In this work we report a novel Nb-doped Na_(0.7)[Ni_(0.3)Co_(0.1)Mn_(0.6)]_(1-x)Nb_(x)O_(2) with significantly suppre ssed voltage decay and enhanced cycling stability.The strong Nb-O bond can efficiently stabilize the TMO fra mework,and the as prepared material demonstrates much lower discharge midpoint voltage decay(0.132 V) than that of pristine one(0.319 V) after 200 cycles.Consequently,a remarkably improved cycling perfo rmance with a capacity retention of 87.9% after 200 cycle at 0.5 C is achieved,showing a 2.4 fold improvement as compared to the control sample Na_(0.7)Ni_(0.3)Co_(0.1)Mn_(0.6)O_(2)(~37% rotation).Even at 2 C,a capacity retention of 68.4% is retained after 500 cycles.Remarkably,the as prepared material can be applied at low temperature of-20℃,showing a capacity retention of 81% as compared to that at room temperature.
基金financially supported by the Beijing Natural Science Foundation(JQ19003)National Key R&D Program of China(grant no.2018YFB0104300)+4 种基金National Natural Science Foundation of China(grant no 51622202,21603009,and 21875007)Beijing Natural Science Foundation(B)(KZ201910005002)Beijing Natural Science Foundation(L182009)Project of Youth Talent Plan of Beijing Municipal Education Commission(CIT&TCD201804013)High-grade discipline construction of Beijing(PXM2019-014204-500031)。
文摘The voltage decay of lithium-rich layered oxides(LLOs)is still one of the key challenges for their application in commercial battery although these materials possess the advantages of high specific capacity and low cost.In this work,the relationship between voltage decay and tap density of LLOs has been focused.The voltage decay can be significantly suppressed with the increasing tap density as well as the homogenization of the primary or secondary particle size of agglomerated spherical LLOs.Experimental results have shown that an extreme small voltage decay of 0.98 m V cycle^(-1)can be obtained through adjusting the tap density of agglomerated spherical LLOs to 1.99 g cm^(-3),in which the size of primary and secondary particles are uniform.Our work offers a new insight towards the voltage decay and capacity fading of LLOs through precursor preparation process,promoting their application in the real battery in the future.
基金funded by the National Natural Science Foundation of China(Grant Nos.22279092 and 5202780089).
文摘Li-rich layered oxide(LRLO)cathodes have been regarded as promising candidates for next-generation Li-ion batteries due to their exceptionally high energy density,which combines cationic and anionic redox activities.However,continuous voltage decay during cycling remains the primary obstacle for practical applications,which has yet to be fundamentally addressed.It is widely acknowledged that voltage decay originates from the irreversible migration of transition metal ions,which usually further exacerbates structural evolution and aggravates the irreversible oxygen redox reactions.Recently,constructing O2-type structure has been considered one of the most promising approaches for inhibiting voltage decay.In this review,the relationship between voltage decay and structural evolution is systematically elucidated.Strategies to suppress voltage decay are systematically summarized.Additionally,the design of O2-type structure and the corresponding mechanism of suppressing voltage decay are comprehensively discussed.Unfortunately,the reported O2-type LRLO cathodes still exhibit partially disordered structure with extended cycles.Herein,the factors that may cause the irreversible transition metal migrations in O2-type LRLO materials are also explored,while the perspectives and challenges for designing high-performance O2-type LRLO cathodes without voltage decay are proposed.
文摘<span style="font-family:Verdana;">This manuscript presents a simple method for excess minority carriers’ lifetime measurement</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">within the base region of p-n junction polycrystalline solar </span><span style="font-family:Verdana;">cell</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">in transient mode.</span><span style="font-family:""> </span><span style="font-family:Verdana;">This work is an experimental transient</span><span style="font-family:Verdana;"> 3-Dimensionnal study.</span><span style="font-family:""> </span><span style="font-family:Verdana;">The magnitude of the magnetic field B is varied from 0 mT to 0.045 mT. Indeed, the solar cell is illuminated by a stroboscopic flash with air mass 1.5</span><span style="font-family:""> </span><span style="font-family:Verdana;">and under magnetic field in transient state.</span><span style="font-family:""> </span><span style="font-family:Verdana;">The experimental details are assumed in a figure. The procedure is outlined by the Open Circuit Voltage Decay analysis. Effective minority carrier life-time is calculated by fitting the linear zone of the transient voltage decay curve</span><span style="font-family:""> </span><span style="font-family:Verdana;">because linear decay is an ideal decay. The kaleidagraph software permits access to the slope of the curve which is inversely proportional to the</span><span style="font-family:""> </span><span style="font-family:Verdana;">lifetime. The external magnetic effects</span><span style="font-family:""> </span><span style="font-family:Verdana;">on minority carriers’ effective lifetime </span><span style="font-family:Verdana;">is</span><span style="font-family:Verdana;"> then</span><span style="font-family:""> </span><span style="font-family:Verdana;">presented and analyzed.</span><span style="font-family:""> </span><span style="font-family:Verdana;">The analysis show</span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;"> that the charge carrier</span><span style="font-family:Verdana;">’</span><span style="font-family:Verdana;">s effective lifetime decrease with the magnetic field increase.</span>
基金the National Natural Science Foundation of China(No.21271145)the National Science Foundation of Hubei Province(No.2015CFB537)+1 种基金the Science and Technology Innovation Committee of Shenzhen Municipality(No.JCYJ20170306171321438)the financial support for this investigation.
文摘Lithium-rich layered oxides(LLOs)have been extensively studied as cathode materials for lithium-ion batteries(LIBs)by researchers all over the world in the past decades due to their high specific capacities and high charge-discharge voltages.However,as cathode materials LLOs have disadvantages of significant voltage and capacity decays during the charge-discharge cycling.It was shown in the past that fine-tuning of structures and compositions was critical to the performances of this kind of materials.In this report,LLOs with target composition of Li1.17Mn0.50Ni0.24Co0.09O2 were prepared by carbonate co-precipitation method with different pH values.X-ray powder diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscope(TEM),and electrochemical impedance spectroscopies(EIS)were used to investigate the structures and morphologies of the materials and to understand the improvements of their electrochemical performances.With the pH values increased from 7.5 to 8.5,the Li/Ni ratios in the compositions decreased from 5.17 to 4.64,and the initial Coulombic efficiency,cycling stability and average discharge voltages were gained impressively.Especially,the material synthesized at pH=8.5 delivered a reversible discharge capacity of 263 mAhg−1 during the first cycle,with 79.0%initial Coulombic efficiency,at the rate of 0.1 C and a superior capacity retention of 94%after 100 cycles at the rate of 1 C.Furthermore,this material exhibited an initial average discharge voltage of 3.65 V,with a voltage decay of only 0.09 V after 50 charge-discharge cycles.The improved electrochemical performances by varying the pH values in the synthesis process can be explained by the mitigation of layered-to-spinel phase transformation and the reduction of solid-electrolyte interface(SEI)resistance.We hope this work can shed some light on the alleviation of voltage and capacity decay issues of the LLOs cathode materials.
基金funded by The Vietnam Ministry of Education and Training under project number B2024-BKA-12.
文摘Minority carrier lifetimesτare a fundamental parameter in semiconductor devices,representing the average time it takes for excess minority carriers to recombine.This characteristic is crucial for understanding and optimizing the performance of semiconductor materials,as it directly influences charge carrier dynamics and overall device efficiency.This work presents a development of PbS thin film deposited by thermal evaporation,at which the PbS thin film was further employed for structural,optical properties,andτ.Especially,the PbS film is probed with an in-house setup for identifying theτ.The procedure is to subject the PbS thin film with a flashlight from a light source with a middle rotating frequency.The derivedτin the in-house characterization setup agrees well with the value from the higher cost characterizing approach of photoluminescence.Therefore,the in-house setup provides additional tools for identifying theτvalues for semiconductor devices.
基金supported by the Applied Basic Research Fund of Guangdong Province(No.2024B1515020071)the National Natural Science Foundation of China(Nos.52371217 and 52150410411)+1 种基金the Science and Technology Innovation Plan Project of Hunan Province(No.2024RC3217)Guangdong Provincial Science and Technology Plan Project(No.2023A0505020009).
文摘The utilization of Li-rich layered oxides(LLOs)as cathodes in high-energy Li-ion batteries is significantly hindered by serious voltage decay and capacity fading due to irreversible oxygen release and transition metal(TM)migration triggered by the lattice strain.Herein,B ions are effectively incorporated into the tetrahedral vacancies situated between TM slab and Li layer of LLOs.The robust B-O bond,along with the low Bader charge of oxygen within BO_(4) tetrahedra,alleviates excessive oxidation of O anions while substantially reinforcing the oxygen framework.Consequently,the B-doped LLO sample exhibits only slight variation in lattice parameters,especially the c-axis,which can be characterized as exhibiting“zero-strain”as supported by in situ XRD data.As a result,the discharge capacity of the B-LLO sample maintains 210.66 mAh·g^(−1) after 300 cycles,with a retention ratio of 90.7%.
基金supported by the National Key R&D Program of China (2016YFB0100301)the National Natural Science Foundation of China (51802020, 51802019)+1 种基金the Beijing Institute of Technology Research Fund Program for Young Scholarsthe Young Elite Scientists Sponsorship Program by CAST (2018QNRC001。
文摘Li-rich layered oxides have become one of the most concerned cathode materials for high-energy lithiumion batteries, but they still suffer from poor cycling stability and detrimental voltage decay, especially at elevated temperature. Herein, we proposed a surface heterophase coating engineering based on amorphous/crystalline Li3 PO4 to address these issues for Li-rich layered oxides via a facile wet chemical method. The heterophase coating layer combines the advantages of physical barrier effect achieved by amorphous Li3 PO4 with facilitated Li+diffusion stemmed from crystalline Li3 PO4. Consequently, the modified Li(1.2) Ni(0.2) Mn(0.6) O2 delivers higher initial coulombic efficiency of 92% with enhanced cycling stability at 55 °C(192.9 mAh/g after 100 cycles at 1 C). More importantly, the intrinsic voltage decay has been inhibited as well, i.e. the average potential drop per cycle decreases from 5.96 mV to 2.99 mV. This surface heterophase coating engineering provides an effective strategy to enhance the high-temperature electrochemical performances of Li-rich layered oxides and guides the direction of surface modification strategies for cathode materials in the future.
基金supported by the National Natural Science Foundation of China(51802019,51802020)the Natural Science Foundation of Chongqing,China(cstc2020jcyj-msxm X0589,cstc2020jcyj-msxm X0654)+2 种基金the Science and Technology Innovation Foundation of Beijing Institute of Technology Chongqing Innovation Center(2020CX5100006)the Young Elite Scientists Sponsorship Program by CAST(2018QNRC001)the support from Beijing Institute of Technology Research Fund Program for Young Scholars。
文摘Lithium-rich manganese-based oxides(LRMOs)have been considered as one of the most promising cathode materials owing to their superior specific capacity and high operating voltage.However,their largescale commercial applications are limited due to problems such as structural instability,voltage decay,and poor cycle stability.Herein,pre-generated oxygen vacancies and oxygen-deficient phase were introduced to Li_(1.2)Mn_(0.6)Ni_(0.2)O_(2)(LMNO)using a facile urea-assisted mixed gas treatment(UMGT)method for facilitating electronic and ionic conductivity,reducing the surface oxygen partial pressure,and suppressing the release of lattice oxygen.Compared with the pristine LMNO material,the UMGT sample modified at 200℃exhibited enhanced discharge capacity,capacity retention,and rate capability.In addition,the Li+diffusion coefficient significantly improved by 50%than that of the reference LMNO.More importantly,the voltage decay was effectively suppressed,with average potential decreasing from 0.53 V(LMNO)to 0.39 V(UMGT-200)after 200 cycles at 1 C.The proposed UMGT method provides an effective strategy to alleviate the phase transition and improve the electrochemical performance for lithium-rich materials,and identifies a promising research direction to inhibit the voltage decay of layered anion redox cathode materials.
基金the support of China Scholarship Council(No.202108430035)G.M.L.acknowledges the Australian Institute of Nuclear Science and Engineering(AINSE)Limited for financial assistance in the form of a Post Graduate Research Award(PGRA)supported by the Australian Research Council(Nos.DP200101862,DP210101486,and FL210100050).
文摘The emergence of anionic redox reactions in layered transition metal oxide cathodes provides practical opportunity to boost the energy density of rechargeable batteries.However,the activation of anionic redox reaction in layered oxides has significant voltage hysteresis and decay that reduce battery performance and limit commercialization.Here,we critically review the up-todate development of anionic redox reaction in layered oxide cathodes,summarize the proposed reaction mechanism,and unveil their connection to voltage hysteresis and decay based on the state-of-the-art progress.In addition,advances associated with various modification approaches to mitigate the voltage hysteresis/decay in layered transition metal oxide cathodes are also included.Finally,we conclude with an appraisal of further research directions including rational design of high-performance layered oxide cathodes with reversible anionic redox reactions and suppressed voltage hysteresis/decay.Findings will be of immediate benefit to the development of layered oxide cathodes for high performance rechargeable batteries.
基金supported by the National Natural Science Foundation of China(22393902,22121005,92372001 and 22393900).This research used resources of the Analysis Platform of New Matter Structure at Nankai University.
文摘Migration of transition metal(TM)ions out of the TM layer is detrimental and unavoidable in lithium-rich layered oxides,which drives in-plane cation migration,O_(2)release and energy loss.Since out-of-plane migration generally occurs through tetrahedral interstices(TLi)in the Li layer,doping TLi sites has been believed as a promising way to block migration pathways at the dopant site.However,with only trace dopants(<1at.%)sparsely distributed in bulk,the ability of isolated dopants to suppress cation disorder in undoped regions remains unknown—largely due to no suitable model materials.Here,combining atomic-scale imaging,X-ray diffraction measurements and first-principles calculations,we demonstrate that W6+ions(0.75at.%)can occupy TLi sites in Li_(1.2)Mn_(0.6)Ni_(0.2)O_(2).TLi-site doping maximizes dopant efficiency,as each single W^(6+)ion exerts a long-range Coulomb repulsion on TM/Li^(+)ions in the TM layer,suppressing both in-plane and out-of-plane cation migration over a broad range(∼2nm diameter),in contrast to local stabilization via other doping techniques.Remarkably,cation ordering is preserved for over 250 cycles,far exceeding the limited structural stability(∼50 cycles)typically achieved with conventional modification strategies.Consequently,O2 release and formation of low-voltage Mn^(3+)/Mn^(4+)redox couple are inhibited,resulting in negligible voltage decay.
基金financially supported by the National Natural Science Foundation of China(Grants 52371217 and 52104304)the Applied Basic Research Fund of Guangdong Province(Grant 2024B1515020071)the Science and Technology Innovation Plan Project of Hunan Province(Grant 2024RC3217).
文摘With the rapid development of the economy,increasing demand for energy storage and electric vehicles require electrode materials for batteries with high energy density,safety,and cyclability,especially for lithium-ion(Li-ion)battery cathodes.However,the understanding of their degradation mechanism remains insufficient due to the complex battery system,the transient nature of the de/lithiation processes,and the lack of advanced characterization techniques.Among these challenges,the mechanism of the Li-rich layered cathode family with high operating voltage and cationic-anionic hybrid charge compensation is particularly difficult to study.For the Li-rich family,their electrochemical mechanisms,for example,oxygen redox reaction and structural evolution,were almost impossible to completely clarify in terms of conventional characterization techniques until the development of various in situ techniques.It is obvious that advanced in situ techniques have accelerated the pace of scientific truth exploration.In this review,these intricate mechanisms revealed by various in situ techniques are summarized to clarify the failure mechanism of Li-rich layered cathodes,and an outlook on the application of these advanced techniques within different battery systems is provided.This review highlights how in situ devices can clearly reveal complex mechanisms and further provides the consultation on characterization techniques for mechanism exploration in various research fields.
基金supported by the National Science Foundation under Grant No.DMR1809372。
文摘Coupled with anionic and cationic redox chemistry,Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries.However,irreversible lattice oxygen loss would exacerbate irreversible transition metal migration,resulting in a drastic voltage decay and capacity degeneration.Herein,a metastable layered Li-excess cathode material,T2-type Li_(0.72)[Li_(0.12)Ni_(0.36)Mn_(0.52)]O_(2),was developed,in which both oxygen stacking arrangement and Li coordination environment fundamentally differ from that in conventional O3-type layered structures.By means of the reversible Li migration processes and structural evolutions,not only can voltage decay be effectively restrained,but also excellent capacity retention can be achieved upon long-term cycling.Moreover,irreversible/reversible anionic/cationic redox activities have been well assigned and quantified by various in/ex-situ spectroscopic techniques,further clarifying the charge compensation mechanism associated with(de)lithiation.These findings of the novel T2 structure with the enhanced anionic redox stability will provide a new scope for the development of high-energy-density Li-rich cathode materials.
文摘High-capacity Li-rich cathode materials can significantly improve the energy density of lithium-ion batteries, which is the key limitation to miniaturization of electronic devices and further improvement of electrical-vehicle mileage. However, severe voltage decay hinders the further commercialization of these materials. Insights into the relationship between the inherent structural stability and external appearance of the voltage decay in high-energy Li-rich cathode materials are critical to solve this problem. Here, we demonstrate that structural evolution can be significantly inhibited by the intentional introduction of certain adventive cations （such as Ni2~） or by premeditated reservation of some of the original Li~ ions in the Li slab in the delithiated state. The voltage decay of Li-rich cathode materials over 100 cycles decreased from 500 to 90 or 40 mV upon introducing Ni2~ or retaining some Li~ ions in the Li slab, respectively. The cations in the Li slab can serve as stabilizers to reduce the repulsion between the two neighboring oxygen layers, leading to improved thermodynamic stability. Meanwhile, the cations also suppress transition metal ion migration into the Li slab, thereby inhibiting structural evolution and mitigating voltage decay. These findings provide insights into the origin of voltage decay in Li-rich cathode materials and set new guidelines for designing these materials for high-energy-density Li-ion batteries.
