文档DESIGNOFNEWCATHODEMATERIALSFORSECONDARYLITHIUMBATTERIES

1、 E. Sivanagi Reddy IntroductionBattery TimelineApplications of batteriesSecondary Lithium ion batteryStructure of batteryCathode materialsAdvances in cathode materialsPromising cathode materials conclusionIntroductionBeginning with the frog-leg experiment by Galvani (1786), followed by the demonstra

2、tions of Volta pile by Volta (1792) and lead-acid accumulator by Plante (1859), several battery chemistries have been developed and realized commercially BatteryA battery is a transducer that converts chemical energy into electrical energy and vice versa.It contains An anode - source A cathode - sin

3、k An electrolyte - the separation of ionic transport and electronic transportTimeline for the major events in the history of batteriesTypes of batteriesPrimary batteries are disposable because their electrochemical reaction cannot be reversed. G negative (irreversible)Secondary batteries are recharg

4、eable, because their electrochemical reaction can be reversed by applying a certain voltage to the battery in the opposite direction of the discharge. G negative, discharge G positive, chargeThe name of “lithium ion battery” was given by T. Nagaura and K. TozawaThe concept of “lithium ion battery” w

5、as firstly introduced by Asahi Kasei Co. LtdLithium ion batteries were first proposed by M. S. Whittingham in the 1970s. Whittingham used TiS2 as the cathode and Lithium metal as the anode.The lithium ion battery (LIB) system has been most successful in recent development of battery.Li is lightest m

6、etal and has one of the highest standard reduction potentials (-3.0 V) Theoretical specific capacity of 3860 Ah/kg in comparison with 820 Ah/kg for Zn and 260 Ah/kg for PbThe first commercial lithium-ion battery was released by Sony in 1991Battery performance is related not only capacity but also to

7、 how fast current can be drawn from it: specific energy (Wh/Kg), energy density (Wh/cm3) and power density (W/Kg) Schematic representation of a Lithium-ion cellUpon charging, lithium ions are released by the cathode and intercalated at the anode. When the cell is discharged, lithium ions are extract

8、ed by the cathode and inserted into the anode.Advantages of Lithium-ion batteriesPOWER High energy density means greater power in a smaller package. 160% greater than NiMH 220% greater than NiCdHIGHER VOLTAGE a strong current allows it to power complex mechanical devices. LONG SHELF-LIFE only 5% dis

9、charge loss per month.10% for NiMH, 20% for NiCdDisadvantages of Lithium-ion batteries - 40% more than NiCd - battery temperature must be monitored from within (which raises the price), and sealed particularly well - when shipping Lithium-ion batteries in bulk (which also raises the price) Class 9 m

10、iscellaneous hazardous material UN Manual of Tests and CriteriaElectrolytesRole 1) ion conductor between cathode and anode 2) generally, Lithium salt dissolved in organic solvent 3) solid electrolyte is also possible if the ion conductivity is high at operating temperature.Requirement 1) Inert 2) Hi

11、gh ionic conductivity, low viscosity 3) low melting point 4) Appropriate concentration of Lithium salt 5) Chemical/thermal stability 6) Low cost 7) Environmental -friendly, non-toxicCommercial electrolytes: LiPF6 in Carbonate solventAnode materials Requirements1) Large capability of Lithium adsorpti

12、on2) High efficiency of charge/discharge3) Excellent cyclability 4) Low reactivity against electrolyte5) Fast reaction rate6) Low cost8) Environmental -friendly, non-toxicCommercial anode materials: Hard Carbon, Graphite materialsOne facet of battery research in which there have been many interestin

13、g discoveries is the area of cathodesA cathode is the electrode of an electrochemical cell at which reduction occursCommon cathode materials of Lithium-ion batteries are the transition metal oxide based compounds such as LiCoO2, LiMn2O4, LiNiO2, LiFePO4A high discharge voltageA high energy capacityA

14、 long cycle lifeA high power densityLight weightLow self-dischargeAbsence of environmentally hazardous elements LiOCoacLiCoO2Method of preparationParticle sizeMorphologyOxygen DeficiencyTemperatureCATHODE MATERIALS Layered oxide cathodes Spinel oxide cathodesZigzag layered LiMnO2 compoundOlivine str

15、ucture of LiMPO4 Other compounds Structures of different cathode materials for lithium ion Structures of different cathode materials for lithium ion batteries: batteries: a)a) LiCoOLiCoO 2 2 layered structure layered structure b) LiMnb) LiMn2 2O O4 4 spinelspinel structure and structure and c)LiFePO

16、c)LiFePO4 4 olivine structure. olivine structure. The green circles are lithium ions, LiThe green circles are lithium ions, Li+ +Structures of cathode materialsAdvantagesAdvantages1.Good Structural Stability-Safety, long 1.Good Structural Stability-Safety, long lifelife2 . Fe and Phosphates are abun

17、dant-Low 2 . Fe and Phosphates are abundant-Low costcost3 . Environmentally friendly-non toxic 3 . Environmentally friendly-non toxic elements elements Disadvantages Disadvantages1.Slow Lithium-ion diffusion1.Slow Lithium-ion diffusion2.Low electronic conductivity2.Low electronic conductivity3.Lower

18、 power capability3.Lower power capabilitya. LiFePO4 Structure Symmetry : Orthorhombic Comparison of cathode materials Ways to Improve Cathode PerformanceIncreasing Energy Density Investigate high voltage cathodes that can deliver all the Lithium in the structure will improve energy densityThin nano-

19、plate materials seem to offer more energy at higher rate 30 nm LiFePO4 nano-plates performed better than thick materialMeso porous LiMn2O4 is another material where there is reduced manganese dissolution Surface Coating of cathodes with either ionically or electronically conductive material AlF3 coa

20、ting on oxide materials is shown to improve performance Composite Cathode Material for Lithium-ion Batteries Based on LiFePO4 SystemSome transition metal (oxy)phosphates and vanadium oxides for lithium batteriesNanostructured cathode materials Raw material cost and environmental impact of large-scal

21、e cells and mass production Production cost of solid-state synthesis using high and long heating processOxygen release and heat generation from the cathode in a fully charged state Sensitivity of safety for charge cutoff voltages Sensitivity of cathode performance for stoichiometry Low practical cap

22、acity of the cathode being half that of a carbonaceous anodeMost abundant is iron, with stable trivalent stateSecond most abundant is titanium, with stable tetravalent stateVanadium, with wide valence change (V 2+ V 5+ ) Molybdenum, with wide valence change (Mo 4+ Mo 6+ )1.Olivine based phosphates s

23、ystems (LiMPO4 where M = Mn, Ni) that can deliver more Lithium as compared to the conventional material LiCoO22. Only very few groups have synthesized LiMnPO4 successfully and this system has a potential around 4.3 V3.LiNiPO4 has a potential around 5.5V. It is believed that Li+ diffusion coefficient

24、 is quite high in nickel phosphate in the range 10-5 m2/s at around room temperature. It should have high thermal stability because the oxygen is covalently bound in the structure4.Novel approaches for synthesis of nanostructured olivines are required to enhance both ionic and electronic conductivity5.LiMn2O4 may be another potential candidate material if the Mn dissolution can