Studies On Preparation And Modification Of High-performance Cathode Materials For Lithium-ion Batteries,and Hybrid Systems Combined With Lead-acid Batteries And Lithium-ion Batteries

Because of the advantages of lithium-ion batteries such as high energy density,excellent cycle performance and high rate discharge performance,lithium-ion batteries cherish broad application prospects in the power,energy storage and other fields.However,the energy density,safety performance and cost of current commercial lithium-ion battery still can not meet people's increasing requirements for improving battery performance,thus limiting its further development.The best preparation programs of cathode material of lithium-ion battery,modification methods of cathode material and hybrid system solutions with lithium iron phosphate batteries and lead-acid battery connected in parallel are studied in this paper.By studying these areas,It is in the hoped that electrochemical performance and application performance of lithium-ion battery will be substantially increased.The main contents are as follows:1,The best preparation process of the precursor of lithium rich cathode material Li_1.5Mn_0.75Ni_0.15Co_0.10O₂ is prepared and the amount of lithium of cathode material combined with the optimum calcination temperature to synthesize the cathode material is studied.Specific protocol and conclusions are as follows:The precursor Mn_0.75Ni_0.15Co_0.10CO₃ with good sphericity and uniform particle size distribution can be achieved by using carbonate coprecipitation method.In this paper influences which pH values?7.2,7.6,8.0?and ammonia content values?0.06,0.12,0.18?exert on particle morphology of precursor is studied.Experiment results show that the best preparation method of the precursor material is achieved when the pH value was 7.6 and ammonia content value is 0.12,from which spherical morphology,smooth particle surface and uniform particle size distribution are obtained.Then spherical lithium rich cathode material is obtained by means which is as follows: the precursor is mixed with lithium carbonate in a state of high temperature solid state reaction.The morphology,structure and electrochemical properties of the cathode material are discussed on the conditions of calcination temperatures?800 ?,850 ?,900 ??and lithium content ratios?Li / [M]=1.4,1.5,1.6?.Experiment results show that the lithium-rich cathode material Li_1.5Mn_0.75Ni_0.15Co_0.10O₂ obtained complete spherical shape,good layered crystal structure when the calcination temperature is 850 ? and lithium content ratio?Li /[M]?is 1.5.Electrochemical performance testing is carried out under condition of charging and discharging voltage varying from 2.0 4.8 V combined with current 0.1 C,initial discharge capacity of cathode achieves 269.6 m Ah / g.The capacity achieves251.2 m Ah / g while voltage range varies from 2.0 4.6 V combined with 0.1 C current.Meanwhile,under condition of 2.0 4.6 V,0.5 C,the capacity retention rate of the sample is still 94.5% after 100 cycles.In addition,the discharge capacity of the material remains 154.4 mAh / g at 5 C rate,which showing excellent rate performance.2,The implementation of CuO coated program for lithium-rich cathode material Li_1.13 [Ni_0.5Mn_0.5]_0.87O₂ is studied,and the impacts to electrochemical properties of cathode materials with different amounts of CuO are analysed,therefor the optimal value of CuO coated amount is found.Specific protocol and conclusions are as follows:Lithium rich cathode material Li_1.13 [Ni0.5Mn0.5] 0.87O₂ is successfully coated with film of CuO layered 4 6 nm by heterogeneous nucleation method.The coated material does not suffer crystal structure changes.Charge-discharge tests showthat although the initial discharge capacity of the coated material is slightly lower than that uncoated,the coated material has excellent cycle characteristics and rate characteristics.Among all the samples,the one with amount of 2 wt.% CuO coated shows the best electrochemical performance with initial discharge capacity of 213.7mAh/g and the first coulombic efficiency of 87.0% under 2.0 4.6 V charge and discharge conditions.By contrast,the first coulombic efficiency of the material uncoated can only achieve 75.7%.In addition,the capacity retention rate of the coated material is 79.3% after 100 cycles at 0.5 C rate and the discharge capacity is 154.8mAh/g at 2 C rate,which are significantly better than the uncoated samples.AC impedance measurements show that the status of the interface between the material and the electrolyte can be effectively improved by CuO coated,and electrochemical impedance is also reduced,thus improving the electrochemical properties of the material.3,Doping methods of Ni and Mn doped on metal element site individually as well as joint doped are studied in order to find out the influences to the electrochemical properties of of LiFePO₄ / C.In this paper,the impact of different amount of doped material is analyzed,which leads to find out the the optimal doping proportion.Specific protocol and conclusions are as follows:In this paper,Ni,Mn doped material of LiFePO₄ / C composites are synthesized by two-stage high temperature solid state reaction method.In all Ni doped samples of LiNi_xFe_1-xPO₄/C?x=0.00,0.01,0.02,0.03,0.04?,LiNi0.02Fe0.98PO₄/C exhibits optimal electrochemical performance among all,and LiMn_0.03Fe_0.97PO₄/C exhibits optimal electrochemical performance among all Mn doped samples of LiMn_yFe_1-yPO₄/C?y=0.00,0.01,0.02,0.03,0.04?,while LiNi_0.02Mn_0.03Fe_0.95PO₄/C which is synthesizedby doping with Ni and Mn combined exhibits better electrochemical performance of higher initial discharging and capacity up to 164.3 mAh/g under condition of charging and discharging voltage of 2.3⁴.2 V at 0.1 C discharging rate and capacity retention rate of 98.7% at 1 C discharging rate after 100 cycles,compared with LiNi0.02Fe0.98PO₄/C which is doped by Ni individually and LiMn_0.03Fe_0.97PO₄/C which is doped by Mn individually.The cyclic voltammetry characteristics test curve?CV?suggests that the polarization and electrochemical impedance of electrode co-doped by Ni and Mn are decreased The experimental results show that theelectrochemical performance of LiFePO₄/C cathode can be improved by suitable metal cation doping.3.2 v 80 Ah lithium iron phosphate battery cells are prepared by co-doped LiNi_0.02Mn_0.03Fe_0.95PO₄/C as cathode material,test results show that the cycle performance and rate performance of the cell are excellent.4,Aparallel hybrid power battery system combined with lithium iron phosphate batteries with cathode of LiNi_0.02Mn_0.03Fe_0.95PO₄/C and lead-acid batteries is studied including theoretical basis,design scheme,system parameter setting and charging and discharging performance of the system,thus a practical method for lower cost alternative to lithium ion batteries is proposed.Test results show as follows:By utilizing the differences of the charging and discharging characteristics between lithium iron phosphate batteries and lead-acid batteries,When discharging,lithium iron phosphate batteries discharge with priority,while the lead-acid batteries are on the contrary,so lead-acid batteries can work in a state of shallow cycle,which can prolong the service life of the lead-acid batteries in the hybrid system,thus the life of the new parallelhybrid power battery system is also prolonged.When hybridbattery system of 12 V 50 Ah charges and discharges in the state of 100 % DOD cycle,its life can still reach 750 times,which is significantly better than the 12 V lead-acid batteries,while the advantage of lithium iron phosphate batteries as large current discharging performance and the advantage of lead-acid batteries as low-cost still retain.The discharging rate capability of Lithium iron phosphate and lead-acid battery hybrid battery system is excellent,test result shows that it can release 100 % of its capacity with 1 C discharging rate and voltage down to 10.5 V,which is significantly better than lead-acid batteries with the capacity of 1 C discharging rate only about 55 %.