高功率型锂离子电池正极材料性能研究

Performance of Cathode Material of High-Power Lithium-Ion Battery

对材料A(LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2))、材料B(LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2))、材料C(LiNi_(0.5)Co_(0.2)Mn_(0.3)O_(2))和材料D(LiNi_(1/3)Co_(1/3)Mn_(1/3)O_(2))4种功率型正极材料的理化性能(晶体结构、晶粒形貌、粒径分布、比表面积、元素含量、残留碱含量、水含量)和电化学性能(首次充放电性能、倍率充放电性能)进行对比分析。结果表明:材料A层状结构良好、结晶性良好,二次颗粒呈球形,且粒度适中,样品累计粒度分布百分数达到50%时所对应的粒径(D_(50))为5.76μm,使用了Mg-Al复合改性策略。电化学性能测试结果表明:材料A的倍率性能和充放电性能明显优于其他3种材料,在极片压实密度分别为2.5,3.0和3.5 g·cm^(-3)时,其3C相对于0.1C倍率放电保持率分别为84.77%,83.34%和84.15%,3C相对于0.1C倍率充电保持率分别为88.78%,86.08%和88.48%;在最优极片压实密度为2.5 g·cm^(-3)时,其在0.1C倍率下,2.5~4.3 V电压区间内首周放电克容量为175.3 mAh·g^(-1),首周充放电效率为92.2%。将材料A作为正极活性材料,2.5 g·cm^(-3)作为压实密度,组装成5.5 Ah软包型锂离子电池,其10C,20C,30C和40C放电相对于1C放电的容量保持率分别为90.71%,89.26%,89%和89.15%,其10C,25C和30C恒流充电容量相对于1C恒流容量充入比分别为93.27%,85.35%和83.33%,表现出优异的倍率充放电性能。

To use energy efficiently and reduce greenhouse gas emission,the market share of electric cars should be increased in the world.With the rapid development of electric vehicles,a demand for lithium-ion batteries with a high-power performance is becoming more and more urgent.Cathode materials have a significant impact on lithium-ion battery power performance.The four cathode materials(marked as Materials A,B,C and D)of high-power lithium-ion batteries were selected by the physicochemical properties and electrochemical performances.The physicochemical properties included crystal structure,grain morphology,particle size distribution,specific surface area,element content,residual alkali content,and water content.The electrochemical properties included first charge and discharge performance and rate charge and discharge performance.X-ray diffraction analysis(XRD)was used to evaluate the crystal structure of the material,and scanning electron microscope(SEM)was used to evaluate the crystal morphology of the material.The main element and impurity element content of the material were evaluated by inductively coupled plasma emission instrument(ICP).The particle size distribution of the material was evaluated by using laser particle size analyzer.The specific surface area meter was used to evaluate the specific surface area of the material.The water content of the materials was evaluated by using the Karl Fischer moisture meter.The acid-base titration method was used to evaluate the residual alkali content of the material.The Material A exhibited good layered structure and crystallinity,and the secondary particles of Material A were spherical with a moderate particle size(5.76μm in average particle size).Material A had the largest particle size and the distribution span,which was conducive to the construction of electrode with good ion channels.In addition,Material A was modified by Mg-Al composite,which might inhibit the mixing of Li^(+)/Ni^(2+)cations,optimize the layered structure,and improve the rate performance of Material A.The specific surface area of Material A(1.033 m^(2)·g^(-1))was large,which was beneficial to the improvement of the diffusion rate of lithium ion.Moreover,Material A had the lowest residual alkali content(2147×10^(-6)),and the water content was less than 500×10^(-6).These excellent properties were of benefit to the construction of high-power lithium-ion batteries.The electrochemical performances of the materials were conducted on the LAND charge-discharge instrument by using the coin half-cells as the carriers.Three compacting densities(2.5,3.0 and 3.5 g·cm^(-3))were prepared from the four materials to assemble coin half-cells.The cathodes consisted of 90%active material,6%carbon black as conductive agent,and 4%polyvinylidene fluoride(PVDF)(mass fraction)as binder.In the coin half-cell,the lithium plate was used as the anode,1 mol·L^(-1)LiPF_(6)(/ethylene carbonate(EC)∶dimethyl carbonate(DMC)=1∶1 by volume)was used as the electrolyte,and the Gelgard 2300 acted as the separator.The coin half-cells were assembled in a glove box filled with high-purity Ar.When the compaction densities of electrode were 2.5,3.0 and 3.5 g·cm^(-3),the ratios of the discharge capacities of Material A of 3C rate to 0.1C rate were 84.77%,83.34%and 84.15%,respectively,and the ratios of the charge capacities of 3C rate to 0.1C rate were 88.78%,86.08%and 88.48%,respectively.The optimal compaction density was 2.5 g·cm^(-3),where the first discharge specific capacity of Material A at 0.1C rate was 175.3 mAh·g^(-1) within the voltage range of 2.5~4.3 V,and the initial Coulomb efficiency was 92.2%.The rate capability and charge-discharge performance of Material A were better than those of the other three materials.Then of Material A was used as the cathode material to assemble a 5.5 Ah lithium-ion pouch battery with a compaction density of 2.5 g·cm^(-3).In the pouch battery,the graphite was used as the anode material.According to the soft-packed lithium-ion battery production process,the cathode and anode active materials were mixed with the conductive agent and the binder in a certain proportion,and the cathode and anode electrodes were manufactured through the processes of homogenization,coating,rolling,slicing,and drying.The batteries were assembled with the cathode and anode electrodes and the separator in between.Finally,the rate performance of the batteries was tested on the Nebulas NEEFLCT-05300-V006 integrated power battery cell test system.The ratios of the discharge capacities of the batteries of 10C,20C,30C and 40C rates relative to 1C rate were 90.71%,89.26%,89.00%and 89.15%,respectively.The ratios of the charge capacities of 10C,25C and 30C rates relative to 1C rate were 93.27%,85.35%and 83.33%.Therefore,the battery assembled by Material A showed an excellent rate capability.In summary,a method was established for performance evaluation and optimization of lithium-ion battery materials.First,the physicochemical properties and electrochemical properties of the materials were evaluated.Then,the lithium-ion full battery was manufactured according to the optimized results,and the relevant electrical properties were tested and verified.This method can be extended to the screening of all lithium-ion battery materials.This paper pointed out the direction for material selection,battery manufacturing and performance improvement and optimization.