Synthesis Of Micro/Nano-structure LiNi_0.5Mn_1.5O₄ And Electrochemical Performance For Lithium-Ion Batteries

With the development of technology like electric vehicles,high power capacity,cycling performance and rate capacity of lithium-ion battery is needed.Spinel LiNi_0.5Mn_1.5O₄ is one of good cathode materials for lithium ion batteries due to its high voltage and high theoretical capacity.In order to solve the existing problems of micro-and nano-structure LiNi_0.5Mn_1.5O₄ material,LiNi_0.5Mn_1.5O₄ materials with hollow micro/nano-structure were prepared with self-template and co-precipitation methods.The micro/nano-structure can improve the electrochemical performance of LiNi_0.5Mn_1.5O₄,especially its cycling performance and rate capacity.This paper is mainly as follows:Firstly,spinel cathode material LiNi_0.5Mn_1.5O₄ was prepared by self-template method.The influence of synthetic process on the properties of products was investigated.Experiment shows that the structure and morphology of precursor MnCO₃ is one of the key factors which influence the LiNi_0.5Mn_1.5O₄ material.Along with the increase of reaction temperature,the crystallinity of MnCO₃ increased and the periticle size increased at first and then decreased.The MnCO₃ prepared at 60oC posses high crystallinity,narrow size distribution,and then stable hollow MnO₂ can be obtained.The special structure of MnO₂ facilitates the formation of hollow micro/nano-strucure of LiNi_0.5Mn_1.5O₄.The crystallinity of LiNi_0.5Mn_1.5O₄ improved with the increase of the calcination temperature.However,the excessively high temperature can produce impurity phase,causing the destruction of spinel structure.The LiNi_0.5Mn_1.5O₄ synthesized at 850oC maintains a complete hollow structure which comprised of numerous nanoparticles.It delivers a reversible capacity of 122.2 mAh·g^-1 and retains 95.83%of the initial capacity after 100 cycles.It still delivers a high specific capacity of 95.14 mAh·g^-1 at 10 C.Annealing process can compensate the loss of oxygen caused at high calcination temperature and decrease the amount of Mn³⁺.The treatment is beneficial to the improvement of performance of LiNi_0.5Mn_1.5O₄ with hollow micro/nano-structure.It is concluded that annealing for 8 h,the synthesized LiNi_0.5Mn_1.5O₄ shows high crystallinity and improved electrical conductivity.The initial specific capacity is improved to 127.3 mAh·g^-1 and capacity retentions is also improved to 95.43%.With the current density increasing to 10 C rate,the discharge capacity is 108.3 mAh·g^-1.Secondly,the cathode material of LiNi_0.5Mn_1.5O₄ was synthesized through co-precipitation method.The influence of synthetic process on the properties of products was investigated.The results show that the precursor which take Na₂CO₃ as the precipitant posses uniform spherical particles with a narrow size distribution.And the stoichiometric and elements homogeneously dispersed of precursor can be obtained.The characteristic of the precursor is beneficial to the formation of the micro/nano-structure of LiNi_0.5Mn_1.5O₄.The LiNi_0.5Mn_1.5O₄ prepared from the precursor exhibits superior electrochemical performance.The cystallinity of LiNi_0.5Mn_1.5O₄ improved along with the temperature increasing.The research results show that the LiNi_0.5Mn_1.5O₄ which calcinated at 850oC has cubic spinel structure with clearly defined octahedral shape and excellent electrochemical property.Its reversible capacity is 120.1 mAh·g^-1 and capacity fading is 5.66%of the initial capacity.The discharge capacity can reach to 98.4 mAh·g^-1 at the rate of 10 C.It is widely believed that the annealing process can improve the performance of the LiNi_0.5Mn_1.5O₄.The LiNi_0.5Mn_1.5O₄ material obtained after annealing for 4 h under700oC exhibits excellent properties,for example,capacity fading is 2.08%of the initial capacity(130.1 mAh·g^-1),the capacity at 10 C is 108.1 mAh·g^-1.After the optimization have been taken,the hollow micro/nano-structure of the LiNi_0.5Mn_1.5O₄ haven been obtained with self-template and co-preicipitation method.All materials exhibit improved performances.The LiNi_0.5Mn_1.5O₄ with hollow micro/nano-structure exhibits higher discharge capacity and rate capacity compared with micro-sturcure LiNi_0.5Mn_1.5O₄.Comparing with nanostructure LiNi_0.5Mn_1.5O₄,the LiNi_0.5Mn_1.5O₄ with hollow micro/nano-structure exhibits superior stability performance.By comparing two methods,co-precipitation is relatively simplicity and relatively low cost.It is considered as one of the most effective ways to synthesize excellent performances of LiNi_0.5Mn_1.5O₄ materials.