不同前驱体制备工艺对高镍三元正极材料LiNi_(0.83)Co_(0.12)Mn_(0.05)O_(2)的影响研究

LiNi_(0.83)Co_(0.12)Mn_(0.05)O_(2)of High Nickel Ternary Cathode Material with Different Precursor Preparation Processes

高镍三元正极材料LiNi_(0.83)Co_(0.12)Mn_(0.05)O_(2)因具有较高的能量密度及较低的成本等优势,逐渐成为电动汽车的主流发展趋势。但是随镍含量的升高,材料电化学性能及热稳定性等越来越差,电池的安全性能面临较大隐患。本文选取不同工艺合成的前驱体为原料制备正极材料,通过X射线衍射(XRD)、扫描电镜(SEM)、差示扫描量热法(DSC)等手段对材料进行表征分析及电化学性能测试等,得出硫酸铵工艺前驱体制备的正极材料截面内部一次颗粒大小差异较小且颗粒与颗粒之间排序较规整,一次颗粒由内向外呈放射状规则分散分布,锂离子通道更通畅。且该工艺前驱体制备的正极材料具有优异的电化学性能,常温循环1000周及高温循环400周(3.0~4.2 V,1.0C/1.0C)容量保持率分别为93.07%和94.46%,另外,该工艺制备的材料热稳定性(DSC)更优,内阻(DCR)更低,电池产气量更小,电池的安全性能有较大改善。这主要是由于硫酸铵工艺前驱体截面具有较均匀的孔隙,且前驱体峰强比值I(001)/I(101)较小,制备的正极材料一次颗粒由内向外呈放射状分散分布,更有利于锂离子的脱出嵌入及降低长循环过程中颗粒与颗粒之间的应力膨胀,减少微裂纹的产生,提升材料的循环性能和安全性能。

With the increasing problems of energy crisis and environmental pollution caused by excessive development of non-renew?able energy such as oil,oil-fueled automotives were gradually replaced by clean energy such as new energy vehicles,and the power batterie industry had ushered in rapid development.Ternary cathode material was the mainstream choice of cathode material for power battery at present.The high nickel ternary cathode materials LiNi_(0.83)Co_(0.12)Mn_(0.05)O_(2)became the mainstream development trend of electric vehicles because of their high energy density and low-cost advantages.However,the electrochemical and safety properties of the materials were limited with the increase of nickel content.The precursor played an important role in the properties of cathode materials.The precursor played an important role in the performance of the cathode material.Aimed at the synthesis of Ni_(0.83)Co_(0.12)Mn_(0.05)(OH)_(2)precursors through co-precipitation by selecting ammonia and ammonium sulfate as complexing agents respectively,and then the cathode materials were prepared,the law of influence of different precursor processes on the properties of the LiNi_(0.83)Co_(0.12)Mn_(0.05)O_(2)cathode materials were compared.The morphology and microstructure of the precursor and anode materials were used to be analyzed by scanning electron microscope(SEM)and focused ion beam(FIB).The crystal structure of the precursor and the cathode materials were analyzed by X ray diffractometer(XRD).The thermal stability of the cathode materials was evaluated by STA449 F3 type thermal analyzer(DSC).Battery test system was used to analyze the material’s 25℃and 45℃cycling performance and direct current(DC)internal resistance(DCR).The Archimedes principle was used to analyze the flatulence and other safety properties of the soft package battery.From the crystal structure and morphology analysis,the precursors synthesized by ammonium sulfate process and ammonia process co-precipitation had good crystal structure and higher crystalinity.The precursor prepared by the ammonium sulfate process had a higher(101)peak intensity and a smaller(001)and(101)peak intensity ratio(I_((001))/I(_(101)))than the ammonia water process,indicating that the crystal growth along the c-axis was stronger and the material layered structure was better.The surface of the precursor prepared by ammonia water process had a plate-like structure thick and uneven in size,with close and irregular contact between the primary particles,the solid structure with no obvious pore could be observed by the electron microscope of sphere cross section.The primary particle shape on the surface of the precursor prepared by ammonium sulfate process was needle bar structure and the primary particle size distribution was uniform,and the contact between the particles was loose,the solid structure with more pores could be observed by the electron microscope of sphere cross section.The crystal structure of cathode materials prepared by two precursors were refined and the constant statistics of cell parameters were obtained,I_((003))/I_((104))ratios of cathode materials prepared by ammonia and ammonium sulfate processes were 2.0896 and 1.9365,in combination with XRD refined Li/Ni mixing data were respectively 0.015 and 0.012,it showed that the lithium-nickel mixing degree of ternary materials prepared by ammonium sulfate precursor was more favorable to the improvement of material properties.The primary particle size of the cathode material prepared by the precursor of ammonia water process was quite different,and the order between the particles.Besides,there were many primary particles of large size,and the large size of the primary particles increased the lithium ions to come out of the embedded channel,which led to the deterioration of cycling performance.However,the size difference of primary particles in the section of the cathode material prepared by ammonium sulfate process is small,the order between particles and particles was more regular,the primary particles were distributed radially from inside to outside,and the lithium ion channel was more smooth.From the battery test system,the cathode material prepared by ammonium sulfate process precursor had better electrochemical performance,the capacity retention rate of the full battery was 93.07%and 94.46%respectively at 25℃for 1000 cycles and at 45℃for 400 cycles(3.0~4.2 V,1.0 C/1.0 C).The change rule of internal resistance(DCR)was simulated by button cell,the relationship between DCR and SOC of the two materials was basically ship-shaped,The DCR of the two process precursors at 20%to 90%SOC was basically the same,the internal resistance gap gradually increased at 0%to 10%SOC and 90%to 100%SOC.At 100%SOC and 0%SOC,the internal resistance of cathode material prepared by ammonia precursor was respectively about 1.22 and 1.35 times that of ammonium sulfate process.From a thermal analyzer,the thermal stability(DSC)of the anode material prepared by ammonium sulfate process was better,and the temperature corresponding to the highest heat release was 8-9℃lower than that prepared by ammonia water process precursor.From the analysis of flatulence performance of soft-packed batteries,under the same high temperature test,the unit gas production of soft battery assembled by ammonium sulfate process was obviously lower than that of ammonia process,which reduced the bulging phenomenon of the battery and greatly improved the safety performance.The results showed that the cross-section of precursor has uniform pores,and the ratio of peak strength to peak strength of precursor I_((001))/I_((101))was small.The primary particles of the cathode materials were distributed radially from the inside to the outside,which was more conducive to the extraction and insertion of lithium ions,reduced the stress expansion between particles and the generation of microcracks during long cycles.At the same time,it could reduce the flatulence rate,reduce the internal resistance,and had better thermal stability,which could comprehensively improve the cycle performance and safety performance of the material.