Research On Preparation And Electrochemical Properties Of Bentonite Silicon-based And Metal Inorganic Salts Anode Materials For Lithium-ion Battery

With the rapid development of world economy,non-renewable fossil fuel?such as coal,oil,natural gas?is increasingly exhausted,which are accompanied with a series of environmental problems.Therefore,the research and development of new electrochemical energy storage system with high capacity,high energy density,long cycle life,safety and pollution-free as well as effective utilization of the natural resources are the inevitable trend of current development.Owing to their high power and energy density,long cycling life and environmental safety,lithium-ion batteries?LIBs?are considered as promising power source candidates for electric and hybrid electric vehicles,space satellites,and large-scale energy storage system.Therefore,the development of anode materials with good electrochemical properties,low-cost,environment friendly is an effective way to improve their utilization as electrode materials in the energy storage system.How to improve the specific capacity,cycling performance of anode materials becomes an academic and industrial research hot topic.In this paper,the bentonite clay was used as matrix and silicon source,and the porous silicon-based materials were obtained by thermic reduction;a series of Li₃V₂?PO₄?₃/C anode materials is synthesized via a rheological phase reaction process.A facile co-precipitation combined hydrothermal method is used to synthesize Pb₃?OH?₂?CO₃?₂ nanosheets.Then SEM,XPS,TEM,XRD and electrochemical performance testers were used to study the relationship between its structures and the electrochemical properties for the electrode materials.Both formation mechanism and lithium storage mechanism were discussed also.According to the electrochemical properties of three kinds of anode materials for lithium-ion batteries,silicon-based anode materials have the most potential for marketization.The main research contents and conclusions are as follows:?1?The bentonite clay was used as matrix and silicon source,and the porous silicon-based materials were obtained by thermic reduction using aluminum,zinc or magnesium powders,respectively.The electrochemical properties of the samples were studied and the results show that silicon-based materials prepared by different kinds of method behaved certain cycling stability and rate capability,and the reduction abilities of magnesium powder is better than those of aluminum powder and zinc powder.When magnesium powder was used as reducing agent,the silicon-based materials prepared maintained discharge capacity of about 550 mAh/g under the current density of 500mA/g and it maintained discharge capacity of about 514 mAh/g under the high current density of 1000 mA/g.When the current density is returned to 100 mA/g,its discharge capacity restored to 660 m Ah/g,which is much lower than that we expected.The results indicate that the silicon-based materials prepared from bentonite clay can be used as promising anode material for lithium-ion battery application and synthesis technology needs to be improved further.?2?The bentonite matrix was obtained by ultrasonic assisted purification,and the porous silicon-based materials were obtained by thermic reduction using aluminum,zinc or magnesium powders,respectively.Carbon coating and additive agents such as manganese acetate or sodium silicate can improve its properties,respectively.When the porous silicon-based materials were used as anode materials,the relationship between their composition and electrochemical properties were studied.The results show that the reduction abilities of aluminum powder and zinc powder are poor,while magnesium powder is best reduced agent among them;the initial discharge capacity for silicon-based material is 1758 m Ah/g.After 300 cycles,the discharge capacity maintained at 750mAh/g under the current density of 100 m A/g.It exhibited high rate capability also and the discharge capacity can be maintained at 720 mAh/g under the current density of 1000mA/g.It is a promising method to prepare porous silicon-based materials as an anode material.When this silicon anode was matched with commercial Li Ni_0.6Co_0.2Mn_0.2O₂cathode,lithium-ion full cell exhibited a capacity of 254.3 mAh/g at 50 m A/g and behaved good cycling performance.?3?A rheological phase reaction method was used to synthesize Li₃V₂?PO₄?₃compound coated by nanocrystalline carbon using LiOH·H₂O,NH₄VO₃,NH₄H₂PO₄and citric acid as raw materials.Li₃V₂?PO₄?₃-V₂O₃/C was synthesized through similar procedures using excess NH₄VO₃ and C₆H₈O₇·H₂O.Both Li₃V₂?PO₄?₃ and Li₃V₂?PO₄?₃-V₂O₃/C were characterized by XRD,TEM and XPS.The electrochemical properties of the synthetic materials were tested by electrochemical performance testers.The results show that the conductivity and electrochemical properties of Li₃V₂?PO₄?₃-V₂O₃/C?LVP-V/C?can be improved.It behaved better electrochemical properties than that of LVP/C.It exhibited the initial discharge capacity of 1083 mAh/g at a current density of 100 mA/g and the discharge capacity still retained at 432 mAh/g after 300 cycles.Furthermore,it performed good rate performance,the discharge capacities of the LVP-V/C sample at currents densities of 100 mA/g,300 mA/g,500mA/g,700 mA/g,1000 m A/g and 2000 m A/g are 1080 mAh/g,470 m Ah/g,427mAh/g,388 mAh/g,375 mAh/g and 340 m Ah/g,respectively.The electrochemical impedance spectroscopy?EIS?showed that the LVP-V/C owned the higher conductivity than that of LVP/C.?4?Citric acid as chelating agent,Li OH·H₂O,NH₄H₂PO₄,NH₄VO₃ as raw material,The lithium vanadium phosphate was synthesized by rheological phase reaction process combined with calcination.The Li₃V₂?PO₄?₃ was doped by Fe³⁺and Y³⁺or both of them to modify its electrochemical properties.The lithium vanadium phosphates such as Li₃V_1.6Fe_0.4?PO₄?₃?Li₃V₁Fe₁?PO₄?₃?Li₃V_0.4Fe_1.6?PO₄?₃?Li₃V_1.9Fe_0.1?PO₄?₃ and Li₃V_1.9Fe_0.08Y_0.02?PO₄?₃ were prepared.The SEM and XRD techniques were used to characterize the morphology and structure for lithium vanadium phosphate samples doped with Fe³⁺and Y³⁺or both of them.The electrochemical properties of the material were tested.Among them,as an anode electrode,the electrochemical performance of Li₃V_1.9Fe_0.1?PO₄?₃ is the best among all samples,at current density of 100 mA/g,the initial discharge capacity is 1256 m Ah/g,after 50 cycles,the discharge capacity maintained at 704.0 mAh/g.As the positive electrode,The electrochemical performance for Li₃V_1.9Fe_0.08Y_0.02?PO₄?₃ is the best among all samples,when the current density was100 m A/g,the initial discharge capacity was 136.8 m Ah/g,after 50 cycles,the discharge capacity is 129.5m Ah/g,much higher than those of pure Li₃V₂?PO₄?₃ and other doped samples.However,using them as symmetric electrodes in the whole lithium ion battery system,it behaved higher capacity and certain cyclic performance,its average operating voltage at the current density of 50 m A/g was 2.2 V,the initial discharge capacity was142.4 mAh/g,After 50 cycles,the discharge capacity could keep at 92.8 mAh/g.?5?Pb₃?OH?₂?CO₃?₂ was synthesized through a hydrothermal process using Na₂CO₃and Pb?NO₃?₂ as raw materials.The prepared materials were modified by carbon coating?carbon sources were glucose,ammonium citrate or recycled tea carbon?and metal ion doping?such as antimony ion,rare earth lanthanum ion and so on?,respectively.The experimental results showed that electrochemical properties for Pb₃?OH?₂?CO₃?₂ doped by antimony is poor and it is not suitable to be used as anode material for lithium-ion batteries.The electrochemical properties for Pb₃?OH?₂?CO₃?₂ doped by iron ion are better than that of lanthanum ion.As an anode electrode material,the Pb₃?OH?₂?CO₃?₂ doped by iron shows good rate performance and cycle performance.Because of carbon coating and doping,the ion transport rate and electronic conductivity could be improved greatly.A lithium-ion full cell exhibited good electrochemical performance when the anode is matched with commercial LiNi_0.6Co_0.2Mn_0.2O₂ cathode.