Studies On Lithium Iron Phosphate Cathode Material For Power Lithium Ion Battery

FePO₄·xH₂O is prepared through precipitation,and rheological phase method is used for the admixture of raw materials.LiFe PO₄/C can be obtained after the high sintering of the admixture.There are three aspects in the synthesis research:1)temperature,p H,stirring mode and so on are studied;Confirming the condition of 65±0.5 ?,p H=1.0 for 20²4 h is the optimum synthetic process;And spherical Fe PO₄·x H₂O?D50?3.5?m,TD?1.4g/cm3?can be obtained.2)Effects of carbon source,organic addition agent and their proportion are studied.For the first time,the use of Analysis gage of stability?AGS?is put forward for the observation of rheological phase stability,to ensure the consistency of different batch.3)Effects of temperature,time,atmosphere and gas-flow rate are studied,confirming powders prepared under argon,at 650 for ?10-12 h represents the best performance,the initial capacity is 155.8m Ah/g,the coulombic efficiency is 98% and the capacity retention is 99% after 100 cls.Three different coating models as fully coated,non-fully coated and noncontinuous fully coated are designed,theoretical calculation results indicate that: 1)carbon coating of LiFe PO₄ is non-fully coated,since the carbon coating only increase the surface area for electron transmission,and do not change the intrinsic ionic or electronic conductivity of LiFe PO₄;2)reducement of particle size is more effective than surface coating for the improvement of rate performance;3)rate performance can no longer be improved when carbon coating reaches a certain proportion.Practical quadrate cells?nominal capacity:7.5Ah?are assembled,using LiFe PO₄/C/graphite.The performance are: 1)the average initial discharge capacity is 7765 m Ah,higher than nominal capacity of 7500 m Ah;2)the capacity retention is 83%?1C charge-discharge?after 5000 cycles;3)cells can suffer as high as 10 C rate during charging,with not obvious resistance changes,and the capacity retention of 10 C and 15 C is 79.72% and 77.01%;4)the initial discharge capacity retnetion at 0?,-10?,-20?,-30 ?are 90.01%,77.33%,72.09%,59.96% separately;5)In hot ovean test,shortage,overcharge and forced –discharge,the cell reveals excellent safety.In summmary,the LiFe PO₄/C compound synthesized by this study owns widespread practical values for its excellent electrochemical performance.