The requirement of energy-storage equipment needs to develop the lithium ion battery(LIB) with high electrochemical performance. The surface modification of commercial LiFePO_4(LFP) by utilizing zeolitic imidazolate f...The requirement of energy-storage equipment needs to develop the lithium ion battery(LIB) with high electrochemical performance. The surface modification of commercial LiFePO_4(LFP) by utilizing zeolitic imidazolate frameworks-8(ZIF-8) offers new possibilities for commercial LFP with high electrochemical performances.In this work, the carbonized ZIF-8(C_(ZIF-8)) was coated on the surface of LFP particles by the in situ growth and carbonization of ZIF-8. Transmission electron microscopy indicates that there is an approximate 10 nm coating layer with metal zinc and graphite-like carbon on the surface of LFP/C_(ZIF-8) sample. The N_2 adsorption and desorptionisotherm suggests that the coating layer has uniform and simple connecting mesopores. As cathode material, LFP/C_(ZIF-8) cathode-active material delivers a discharge specific capacity of 159.3 m Ah g^(-1) at 0.1 C and a discharge specific energy of 141.7 m Wh g^(-1) after 200 cycles at 5.0 C(the retention rate is approximate 99%). These results are attributed to the synergy improvement of the conductivity,the lithium ion diffusion coefficient, and the degree of freedom for volume change of LFP/C_(ZIF-8) cathode. This work will contribute to the improvement of the cathode materials of commercial LIB.展开更多
Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles(4-6 nm) were fabricated using bimodal mesoporous carbon(BMC) as continuous conductive networks. The unique pore structure of ...Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles(4-6 nm) were fabricated using bimodal mesoporous carbon(BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO4, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO4 and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g-1at 0.1 C of the high loading electrode and 42 mAh·g-1at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO4 loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO4 displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.展开更多
With the number of decommissioned electric vehicles increasing annually,a large amount of discarded power battery cathode material is in urgent need of treatment.However,common leaching methods for recovering metal sa...With the number of decommissioned electric vehicles increasing annually,a large amount of discarded power battery cathode material is in urgent need of treatment.However,common leaching methods for recovering metal salts are economically inefficient and polluting.Meanwhile,the recycled material obtained by lithium remediation alone has limited performance in cycling stability.Herein,a short method of solid-phase reduction is developed to recover spent LiFePO4 by simultaneously introducing Mg2+ions for hetero-atom doping.Issues of particle agglomeration,carbon layer breakage,lithium loss,and Fe3+defects in spent LiFePO4 are also addressed.Results show that Mg2+addition during regeneration can remarkably enhance the crystal structure stability and improve the Li+diffusion coefficient.The regenerated LiFePO4 exhibits significantly improved electrochemical performance with a specific discharge capacity of 143.2 mAh·g^(−1)at 0.2 C,and its capacity retention is extremely increased from 37.9%to 98.5%over 200 cycles at 1 C.Especially,its discharge capacity can reach 95.5 mAh·g^(−1)at 10 C,which is higher than that of spent LiFePO4(55.9 mAh·g^(−1)).All these results show that the proposed regeneration strategy of simultaneous carbon coating and Mg2+doping is suitable for the efficient treatment of spent LiFePO4.展开更多
In the search for improved materials for rechargeable lithium batteries, LiFePO4 offers interesting possibilities because of its low raw materials cost, environmental friendliness and safety. The main drawback with us...In the search for improved materials for rechargeable lithium batteries, LiFePO4 offers interesting possibilities because of its low raw materials cost, environmental friendliness and safety. The main drawback with using the material is its poor electronic conductivity and this limitation has to be overcome. Here Al-doped LiFePO4/C composite cathode materials were prepared by a polymer-network synthesis technique. Testing of X-ray diffraction, charge-discharge, and cyclic voltammetry were carried out for its performance. Results show that Al-doped LiFePO4/C composite cathode materials have a high initial capacity, good cycle stability and excellent low temperature performance. The electrical conductivity of LiFePO4 material can be obviously improved by doping Al. The better electrochemical performances of Al-doped LiFePO4/C composite cathode materials have a connection with its conductivity.展开更多
The state of charge (SOC) and state of health (SOH) are two of the most important parameters of Li-ion batteries in industrial production and in practical applications. The real-time estimation for these two param...The state of charge (SOC) and state of health (SOH) are two of the most important parameters of Li-ion batteries in industrial production and in practical applications. The real-time estimation for these two parameters is crucial to realize a safe and reliable battery application. However, this is a great problem for LiFePO4 batteries due to the large constant potential plateau in the charge/discharge process. Here we propose a combined SOC and SOH co-estimation method based on the experimental test under the simulating electric vehicle working condition. A first-order resistance-capacitance equivalent circuit is used to model the battery cell, and three parameter values, ohmic resistance (Rs), parallel resistance (Rp) and parallel capacity (Cp), are identified from a real-time experimental test. Finally we find that Rp and Cp could be utilized to make a judgement on the SOIl. More importantly, the linear relationship between Cp and the SOC is established to make the estimation of the SOC for the first time.展开更多
Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precu...Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precursors of LiFePO4, LiFePO4/C composite and the resultant products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and the electrochemical performances were investigated by galvanostatic charge and discharge tests. The precursors composed of amorphous Fe3(PO4)2·xH2O and crystalline Li3PO4 obtained in the co-precipitation processing have a sphere-like morphology. The spherical LiFePO4 derived from the calcinations of the precursor at 700 ℃ for 10 h in a reduction atmosphere shows a discharge capacity of 119 mAh·g-1 at the C/10 rate, while the LiFePO4/C composite with 10wt.% carbon addition exhibits a discharge capacity of 140 mAh·g-1. The electrochemical performances indicate that the LiFePO4/C composite has a higher specific capacity and a more stable cycling performance than the bare olivine LiFePO4 due to the carbon addition enhancing the electronic conductivity.展开更多
Carbon nanotubes (CNTs) and acetylene black (AB) were dispersed synchronously or separately between LiFePO4 (LFP) particles as conducting agents during the course of manufacture of LiFePO4 cathodes. The morphology and...Carbon nanotubes (CNTs) and acetylene black (AB) were dispersed synchronously or separately between LiFePO4 (LFP) particles as conducting agents during the course of manufacture of LiFePO4 cathodes. The morphology and electrochemical performances of as-prepared LiFePO4 were evaluated by means of transmission electron microscopy (TEM), charge-discharge test, electrochemical impedance spectroscope (EIS) and cyclic voltammetry (CV). CNTs contribute to the interconnection of the isolated LiFePO4 or carbon particles. For the CNTs-modified LiFePO4, it exhibits excellent performance in terms of both specific capacity and cycle life. The initial discharge capacity is 147.9 mA·h/g at 0.2C rate and 134.2 mA·h/g at 1C rate, keeping a capacity retention ratio of 97% after 50 cycles. The results from EIS indicate that the impedance value of the solid electrolyte interface decreases. The cyclic voltammetric peak profiles is more symmetric and spiculate and there are fewer peaks. CNTs are promising conductive additives candidate for high-power Li-ion batteries.展开更多
Olivine lithium iron phosphate(Li Fe PO4) is considered as a promising cathode material for high power density lithium ion battery due to its high capacity, long cycle life, environmental friendly, low cost, and safet...Olivine lithium iron phosphate(Li Fe PO4) is considered as a promising cathode material for high power density lithium ion battery due to its high capacity, long cycle life, environmental friendly, low cost, and safety consideration. The theoretical capacity of Li Fe PO4 based on one electron reaction is 170 m Ah g-1at the stable voltage plateau of 3.5 V vs. Li/Li+. However, the instinct drawbacks of olivine structure induce a poor rate performance, resulting from the low lithium ion diffusion rate and low electronic conductivity.In this review, we summarize the methods for enhancing the rate performance of Li Fe PO4 cathode materials,including carbon coating, elements doping, preparation of nanosized materials, porous materials and composites,etc. Meanwhile, the advantages and disadvantages of above methods are also discussed.展开更多
LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical perf...LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical performance was investigated in terms of cycling behavior. There has a special micro-morphology via the process, which is favorable to electrochemical properties. The discharge capacity of the LiFePO4.C composite was 170 mAh g-1, equal to the theoretical specific capacity at 0.1 C rate. At 4 C current density, the specific capacity was about 80 mAh g-1, which can satisfy for transportation applications if having a more flat discharge flat.展开更多
The work distills the main mechanisms during the lithium insertion/extraction of LiFePOcathode materials. The "diffusion-controlled" and "phase-boundary controlled" mechanism are especially illustr...The work distills the main mechanisms during the lithium insertion/extraction of LiFePOcathode materials. The "diffusion-controlled" and "phase-boundary controlled" mechanism are especially illustrated. Meanwhile, some recent observation and analyses by in-situ or in operando on the Li-insertion/extraction of LiFePOare summarized and prospected.展开更多
As the byproduct of TiO2 industrial production, impure FeSO4.7H2O was used for the synthesis of LiFePO4. With the purified solution of FeSO4-7H2O, FePO4.xH2O was prepared by a normal titration method and a controlled ...As the byproduct of TiO2 industrial production, impure FeSO4.7H2O was used for the synthesis of LiFePO4. With the purified solution of FeSO4-7H2O, FePO4.xH2O was prepared by a normal titration method and a controlled crystallization method, respectively. Then LiFePO4 materials were synthesized by calcining the mixture of FePO4,xH2O, LizCO3, and glucose at 700℃ for 10 h in flowing Ar. The results indicate that the elimination of FeSO4.TH2O impurities reached over 95%, and using FePO4-xH2O prepared by the controlled crystallization method, the obtained LiFePO4 material has fine and sphere-like particles. The material delivers a higher initial discharge specific capacity of 149 mAh.g^-1 at a current density of 0.1C rate (1C = 170 mA.g^-0); the discharge specific capacity also maintains above 120 rnAh.g^-1 after 100 cycles even at 2C rate. Thus, the employed processing is promising for easy control, low cost of raw material, and high electrochemical performance of the prepared material.展开更多
LiFePO4 cathode material was synthesized by a solid-state reaction using doping several elements (Nb5 + ,Zr4 + ). The starting materials were mixed with a high-efficient sander and treated thermally under flowing N2. ...LiFePO4 cathode material was synthesized by a solid-state reaction using doping several elements (Nb5 + ,Zr4 + ). The starting materials were mixed with a high-efficient sander and treated thermally under flowing N2. The samples were characterized by X-ray diffraction (XRD), field-emission gun electron microscopy (FEG), and their electrochemical performance was investigated in the term of cycling behavior. Room temperature discharge capacity about 140.6 mA·h·g-1 was obtained at C/5 rate.展开更多
LiFePOa/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 atmosphere with polyvinyl alcohol (PVA) as the carbon source. The influences of carbon content on the m...LiFePOa/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 atmosphere with polyvinyl alcohol (PVA) as the carbon source. The influences of carbon content on the microstructure and battery performance were investigated. Single LiFePO4 phase and amorphous carbon can be found in the products. A special micro-morphology of the optimum sample was observed. The discharge capacity of the cell with the optimum cathode was 135 mAh.g^-1, close to the charge capacity of 153 mAh.g^-1 at 17 mA.g^-1. The influence of ambient temperature on the cell capacity was investigated. The temperature dependence of its electrochemical characteristic was evaluated by using AC impedance spectroscopy. A new equivalent circuit based on the charge and mass transfer control process in an electrode was proposed to fit the obtained AC impedance spectra. The tendency of every element in the equivalent circuit was used to interpret the temperature dependence of the capacity of the optimum cathode.展开更多
A compound "vacuum firing and water quenching" technique was presented in the synthesis of LiFeP04 cathode powder. The sample was prepared by heating the we-decomposed precursor mixtures sealed in vacuum quartz-tube...A compound "vacuum firing and water quenching" technique was presented in the synthesis of LiFeP04 cathode powder. The sample was prepared by heating the we-decomposed precursor mixtures sealed in vacuum quartz-tube, followed by water quenching at the sintering temperature. The results indicate that using the "fast quenching" treatment can succeed in controlling overgrowth of the grain size of final product and improving its utilization ratio of active material. The sample synthesized by this technique has the high reversible discharge specific capacity and good cyclic electrochemical performance.展开更多
Phspho-olivine Li Fe PO4 was synthesized from the relatively insoluble lithium source Li2CO3, proper iron and phosphorus sources(n(Li):n(Fe):n(P)=1:1:1) by a novel hydrothermal method. Afterwards, the opti...Phspho-olivine Li Fe PO4 was synthesized from the relatively insoluble lithium source Li2CO3, proper iron and phosphorus sources(n(Li):n(Fe):n(P)=1:1:1) by a novel hydrothermal method. Afterwards, the optimal sample was mixed with glucose and two-step calcinated(500 ℃ and 750 ℃) under high-purity N2 to obtain the Li Fe PO4/C composite. The resultant samples were characterized by X-ray diffraction(XRD), atomic absorption spectrometry(AAS), scanning electron microscops(SEM), transmission electron microscopy(TEM), energy dispersive spectrometry(EDS), elementary analysis(EA) and electrochemical tests. The results show that the optimal reaction condition is to set the reactant concentration at 0.5 mol·L^-1, the reaction temperature at 180 ℃ for 16 h duration. During the reaction course, an intermediate product NH4 Fe PO4·H2O was first synthesized, and then it reacted with Li+ to form Li Fe PO4. The optimized Li Fe PO4 sample with an average particle size(300 to 500 nm) and regular morphology exhibits a relatively high discharge capacity of 84.95 m Ah· g^-1 at the first charge-discharge cycle(0.1C, 1C=170 m A·g^-1). Moreover, the prepared Li Fe PO4/C composite shows a high discharge capacity of 154.3 m Ah·g^-1 at 0.1C and 128.2 m Ah·g^-1 even at 5C. Besides it has good reversibility and stability in CV test.展开更多
A LiFePO4/C composite was synthesized by a simple solid-state reaction method using glucose as reductive agent and carbon source and FePO4 as precursor, which was prepared by introduction of Na3PO4 as phosphorus sourc...A LiFePO4/C composite was synthesized by a simple solid-state reaction method using glucose as reductive agent and carbon source and FePO4 as precursor, which was prepared by introduction of Na3PO4 as phosphorus source and pH regulator in order to pursue lower cost and environmental protection. The structure and morphology of FePO4 and LiFePO4/C were investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM). Furthermore, electrochemical performance of LiFePO4/C was investigated by galvanostatic charge–discharge tests and cyclicvoltammogram(CV). The results indicate that FePO4 obtained has a small particle size and uniform particle distribution, which is demonstrated to be applicable as the iron source to synthesize LiFePO4/C. Prepared LiFePO4/C shows an excellent rate capability and cycle performance. At rates of 0.1 C, 0.2 C, 1 C and 2 C, the initial discharge capacities of 161, 158, 145 and 120 mAh/g were achieved, respectively and the discharge capacity is 154, 153, 140 and 116 mAh/g after 400 cycles. The employed method of preparing FePO4 by introduction of Na3PO4 has advantages such as low cost, safe raw material, environmental benign and recyclable products, which is suitable for industrial production.展开更多
基金supported by the Scientific and Technological Development Project of the Beijing Education Committee(No.KZ201710005009)
文摘The requirement of energy-storage equipment needs to develop the lithium ion battery(LIB) with high electrochemical performance. The surface modification of commercial LiFePO_4(LFP) by utilizing zeolitic imidazolate frameworks-8(ZIF-8) offers new possibilities for commercial LFP with high electrochemical performances.In this work, the carbonized ZIF-8(C_(ZIF-8)) was coated on the surface of LFP particles by the in situ growth and carbonization of ZIF-8. Transmission electron microscopy indicates that there is an approximate 10 nm coating layer with metal zinc and graphite-like carbon on the surface of LFP/C_(ZIF-8) sample. The N_2 adsorption and desorptionisotherm suggests that the coating layer has uniform and simple connecting mesopores. As cathode material, LFP/C_(ZIF-8) cathode-active material delivers a discharge specific capacity of 159.3 m Ah g^(-1) at 0.1 C and a discharge specific energy of 141.7 m Wh g^(-1) after 200 cycles at 5.0 C(the retention rate is approximate 99%). These results are attributed to the synergy improvement of the conductivity,the lithium ion diffusion coefficient, and the degree of freedom for volume change of LFP/C_(ZIF-8) cathode. This work will contribute to the improvement of the cathode materials of commercial LIB.
基金supported by the National Natural Science Foundation of China (NSFC 21103184)the Ph.D.Programs Foundation (20100041110017) of Ministry of Education of Chinathe Fundamental Research Funds for the Central Universities
文摘Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles(4-6 nm) were fabricated using bimodal mesoporous carbon(BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO4, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO4 and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g-1at 0.1 C of the high loading electrode and 42 mAh·g-1at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO4 loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO4 displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.
基金supported by the Science and Technology Innovation Program of Hunan Province(No.2020SK2007)the Natural Science Foundation of Hunan Province(No.2019JJ50814)+2 种基金the Fundamental Research Funds for the Central Universities of Central South University(No.1053320211765)the Science and Technology Planning Project of Guangdong Province of China(No.2017B030314046)Guangdong Academy of Sciences for Innovation Capacity Building(No.2016GDASRC0201).
文摘With the number of decommissioned electric vehicles increasing annually,a large amount of discarded power battery cathode material is in urgent need of treatment.However,common leaching methods for recovering metal salts are economically inefficient and polluting.Meanwhile,the recycled material obtained by lithium remediation alone has limited performance in cycling stability.Herein,a short method of solid-phase reduction is developed to recover spent LiFePO4 by simultaneously introducing Mg2+ions for hetero-atom doping.Issues of particle agglomeration,carbon layer breakage,lithium loss,and Fe3+defects in spent LiFePO4 are also addressed.Results show that Mg2+addition during regeneration can remarkably enhance the crystal structure stability and improve the Li+diffusion coefficient.The regenerated LiFePO4 exhibits significantly improved electrochemical performance with a specific discharge capacity of 143.2 mAh·g^(−1)at 0.2 C,and its capacity retention is extremely increased from 37.9%to 98.5%over 200 cycles at 1 C.Especially,its discharge capacity can reach 95.5 mAh·g^(−1)at 10 C,which is higher than that of spent LiFePO4(55.9 mAh·g^(−1)).All these results show that the proposed regeneration strategy of simultaneous carbon coating and Mg2+doping is suitable for the efficient treatment of spent LiFePO4.
基金This work was financially supported by the Middle Age and Youth Backbone Teacher Project (2004) of Henan Province, China.
文摘In the search for improved materials for rechargeable lithium batteries, LiFePO4 offers interesting possibilities because of its low raw materials cost, environmental friendliness and safety. The main drawback with using the material is its poor electronic conductivity and this limitation has to be overcome. Here Al-doped LiFePO4/C composite cathode materials were prepared by a polymer-network synthesis technique. Testing of X-ray diffraction, charge-discharge, and cyclic voltammetry were carried out for its performance. Results show that Al-doped LiFePO4/C composite cathode materials have a high initial capacity, good cycle stability and excellent low temperature performance. The electrical conductivity of LiFePO4 material can be obviously improved by doping Al. The better electrochemical performances of Al-doped LiFePO4/C composite cathode materials have a connection with its conductivity.
基金Supported by the Guangdong Innovation Team Project under Grant No 2013N080the Peacock Plan of Shenzhen Science and Technology Research under Grant No KYPT20141016105435850
文摘The state of charge (SOC) and state of health (SOH) are two of the most important parameters of Li-ion batteries in industrial production and in practical applications. The real-time estimation for these two parameters is crucial to realize a safe and reliable battery application. However, this is a great problem for LiFePO4 batteries due to the large constant potential plateau in the charge/discharge process. Here we propose a combined SOC and SOH co-estimation method based on the experimental test under the simulating electric vehicle working condition. A first-order resistance-capacitance equivalent circuit is used to model the battery cell, and three parameter values, ohmic resistance (Rs), parallel resistance (Rp) and parallel capacity (Cp), are identified from a real-time experimental test. Finally we find that Rp and Cp could be utilized to make a judgement on the SOIl. More importantly, the linear relationship between Cp and the SOC is established to make the estimation of the SOC for the first time.
基金This work was financially supported by the National Natural Science Foundation of China (No.50134020)
文摘Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precursors of LiFePO4, LiFePO4/C composite and the resultant products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and the electrochemical performances were investigated by galvanostatic charge and discharge tests. The precursors composed of amorphous Fe3(PO4)2·xH2O and crystalline Li3PO4 obtained in the co-precipitation processing have a sphere-like morphology. The spherical LiFePO4 derived from the calcinations of the precursor at 700 ℃ for 10 h in a reduction atmosphere shows a discharge capacity of 119 mAh·g-1 at the C/10 rate, while the LiFePO4/C composite with 10wt.% carbon addition exhibits a discharge capacity of 140 mAh·g-1. The electrochemical performances indicate that the LiFePO4/C composite has a higher specific capacity and a more stable cycling performance than the bare olivine LiFePO4 due to the carbon addition enhancing the electronic conductivity.
基金supported by the National Science Foundation for Young Scholars (No. 11004032)National Natural Science Foundation of China (No. 11074039)Fujian Province Science Foundation for Young Scholars (No.2008F3039)
基金Project(06B002)supported by Scientific Research Fund of Hunan Provincial Education Department of ChinaProject(09JJ3092)supported by Hunan Provincial Natural Science Foundation of ChinaProject(2008FJ3008)supported by the Planned Science and Technology Project of Hunan Province of China
文摘Carbon nanotubes (CNTs) and acetylene black (AB) were dispersed synchronously or separately between LiFePO4 (LFP) particles as conducting agents during the course of manufacture of LiFePO4 cathodes. The morphology and electrochemical performances of as-prepared LiFePO4 were evaluated by means of transmission electron microscopy (TEM), charge-discharge test, electrochemical impedance spectroscope (EIS) and cyclic voltammetry (CV). CNTs contribute to the interconnection of the isolated LiFePO4 or carbon particles. For the CNTs-modified LiFePO4, it exhibits excellent performance in terms of both specific capacity and cycle life. The initial discharge capacity is 147.9 mA·h/g at 0.2C rate and 134.2 mA·h/g at 1C rate, keeping a capacity retention ratio of 97% after 50 cycles. The results from EIS indicate that the impedance value of the solid electrolyte interface decreases. The cyclic voltammetric peak profiles is more symmetric and spiculate and there are fewer peaks. CNTs are promising conductive additives candidate for high-power Li-ion batteries.
基金supported by the Foundation on the Creative Research Team Construction Promotion Pro ject of Beijing Municipal Institutions
文摘Olivine lithium iron phosphate(Li Fe PO4) is considered as a promising cathode material for high power density lithium ion battery due to its high capacity, long cycle life, environmental friendly, low cost, and safety consideration. The theoretical capacity of Li Fe PO4 based on one electron reaction is 170 m Ah g-1at the stable voltage plateau of 3.5 V vs. Li/Li+. However, the instinct drawbacks of olivine structure induce a poor rate performance, resulting from the low lithium ion diffusion rate and low electronic conductivity.In this review, we summarize the methods for enhancing the rate performance of Li Fe PO4 cathode materials,including carbon coating, elements doping, preparation of nanosized materials, porous materials and composites,etc. Meanwhile, the advantages and disadvantages of above methods are also discussed.
文摘LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical performance was investigated in terms of cycling behavior. There has a special micro-morphology via the process, which is favorable to electrochemical properties. The discharge capacity of the LiFePO4.C composite was 170 mAh g-1, equal to the theoretical specific capacity at 0.1 C rate. At 4 C current density, the specific capacity was about 80 mAh g-1, which can satisfy for transportation applications if having a more flat discharge flat.
基金supported by the National Natural Science Foundation of China(No.51504196)Key Research and Development Plan of Shaanxi Province(No.2017ZDXM-GY-039)
文摘The work distills the main mechanisms during the lithium insertion/extraction of LiFePOcathode materials. The "diffusion-controlled" and "phase-boundary controlled" mechanism are especially illustrated. Meanwhile, some recent observation and analyses by in-situ or in operando on the Li-insertion/extraction of LiFePOare summarized and prospected.
基金supported by the National Key Technology R & D Program of China (No.2007BAE12B01-1)the National Natural Science Foundation of China (No.50604018)
文摘As the byproduct of TiO2 industrial production, impure FeSO4.7H2O was used for the synthesis of LiFePO4. With the purified solution of FeSO4-7H2O, FePO4.xH2O was prepared by a normal titration method and a controlled crystallization method, respectively. Then LiFePO4 materials were synthesized by calcining the mixture of FePO4,xH2O, LizCO3, and glucose at 700℃ for 10 h in flowing Ar. The results indicate that the elimination of FeSO4.TH2O impurities reached over 95%, and using FePO4-xH2O prepared by the controlled crystallization method, the obtained LiFePO4 material has fine and sphere-like particles. The material delivers a higher initial discharge specific capacity of 149 mAh.g^-1 at a current density of 0.1C rate (1C = 170 mA.g^-0); the discharge specific capacity also maintains above 120 rnAh.g^-1 after 100 cycles even at 2C rate. Thus, the employed processing is promising for easy control, low cost of raw material, and high electrochemical performance of the prepared material.
文摘LiFePO4 cathode material was synthesized by a solid-state reaction using doping several elements (Nb5 + ,Zr4 + ). The starting materials were mixed with a high-efficient sander and treated thermally under flowing N2. The samples were characterized by X-ray diffraction (XRD), field-emission gun electron microscopy (FEG), and their electrochemical performance was investigated in the term of cycling behavior. Room temperature discharge capacity about 140.6 mA·h·g-1 was obtained at C/5 rate.
基金This work was financially supported by the National Natural Science Foundation of China (No.50372003, 50472005)Tsinghua University Fundamental Research Fundation (No.JC2003040)
文摘LiFePOa/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 atmosphere with polyvinyl alcohol (PVA) as the carbon source. The influences of carbon content on the microstructure and battery performance were investigated. Single LiFePO4 phase and amorphous carbon can be found in the products. A special micro-morphology of the optimum sample was observed. The discharge capacity of the cell with the optimum cathode was 135 mAh.g^-1, close to the charge capacity of 153 mAh.g^-1 at 17 mA.g^-1. The influence of ambient temperature on the cell capacity was investigated. The temperature dependence of its electrochemical characteristic was evaluated by using AC impedance spectroscopy. A new equivalent circuit based on the charge and mass transfer control process in an electrode was proposed to fit the obtained AC impedance spectra. The tendency of every element in the equivalent circuit was used to interpret the temperature dependence of the capacity of the optimum cathode.
基金the financial support from the National Natural Science Foundation of China(No.50604018)and from Central South University.
文摘A compound "vacuum firing and water quenching" technique was presented in the synthesis of LiFeP04 cathode powder. The sample was prepared by heating the we-decomposed precursor mixtures sealed in vacuum quartz-tube, followed by water quenching at the sintering temperature. The results indicate that using the "fast quenching" treatment can succeed in controlling overgrowth of the grain size of final product and improving its utilization ratio of active material. The sample synthesized by this technique has the high reversible discharge specific capacity and good cyclic electrochemical performance.
基金Funded by the National Natural Science Foundation of China(No.51004074)
文摘Phspho-olivine Li Fe PO4 was synthesized from the relatively insoluble lithium source Li2CO3, proper iron and phosphorus sources(n(Li):n(Fe):n(P)=1:1:1) by a novel hydrothermal method. Afterwards, the optimal sample was mixed with glucose and two-step calcinated(500 ℃ and 750 ℃) under high-purity N2 to obtain the Li Fe PO4/C composite. The resultant samples were characterized by X-ray diffraction(XRD), atomic absorption spectrometry(AAS), scanning electron microscops(SEM), transmission electron microscopy(TEM), energy dispersive spectrometry(EDS), elementary analysis(EA) and electrochemical tests. The results show that the optimal reaction condition is to set the reactant concentration at 0.5 mol·L^-1, the reaction temperature at 180 ℃ for 16 h duration. During the reaction course, an intermediate product NH4 Fe PO4·H2O was first synthesized, and then it reacted with Li+ to form Li Fe PO4. The optimized Li Fe PO4 sample with an average particle size(300 to 500 nm) and regular morphology exhibits a relatively high discharge capacity of 84.95 m Ah· g^-1 at the first charge-discharge cycle(0.1C, 1C=170 m A·g^-1). Moreover, the prepared Li Fe PO4/C composite shows a high discharge capacity of 154.3 m Ah·g^-1 at 0.1C and 128.2 m Ah·g^-1 even at 5C. Besides it has good reversibility and stability in CV test.
基金Funded by Natural Science Foundation of Hebei Province(No E2017409004)Department of Education of Hebei Province(No QN2016224)
文摘A LiFePO4/C composite was synthesized by a simple solid-state reaction method using glucose as reductive agent and carbon source and FePO4 as precursor, which was prepared by introduction of Na3PO4 as phosphorus source and pH regulator in order to pursue lower cost and environmental protection. The structure and morphology of FePO4 and LiFePO4/C were investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM). Furthermore, electrochemical performance of LiFePO4/C was investigated by galvanostatic charge–discharge tests and cyclicvoltammogram(CV). The results indicate that FePO4 obtained has a small particle size and uniform particle distribution, which is demonstrated to be applicable as the iron source to synthesize LiFePO4/C. Prepared LiFePO4/C shows an excellent rate capability and cycle performance. At rates of 0.1 C, 0.2 C, 1 C and 2 C, the initial discharge capacities of 161, 158, 145 and 120 mAh/g were achieved, respectively and the discharge capacity is 154, 153, 140 and 116 mAh/g after 400 cycles. The employed method of preparing FePO4 by introduction of Na3PO4 has advantages such as low cost, safe raw material, environmental benign and recyclable products, which is suitable for industrial production.