Review on LiNi0.5Mn1.5O4 (LNMO) as a Promise 5V-class Cathode Material for Li-ion Batteries

With respect to the shortcoming the unrenewable energy sources in recent years, Li-ion batteries as a high energy, high voltage, high specific capacity, and long cycle life energy storage device had attracted the customer’s attention. Towards the better electrochemical performance, a high capacity anode, a high energy and high rate cathode, and a wide-potential electrolyte are required. Until now, numerous anode materials such as traditional graphite, Sn, Al, Ge, LTO as a safe electrode, and Si with 4200 mAh/g theoretical specific capacity were introduced. Nevertheless, cathode electrode as a Li-ion source plays a critical role in the supplying energy. Recently, various high capacity or high voltage cathode materials including layered oxides, phosphates, sulfates, borates, and silicates were developed to access up to 5V operating voltage and 400 mAh/g specific capacity. One of the promise 5V-class cathode materials is LiNi0.5Mn1.5O4 (LNMO) with the discharge voltage of 4.7-4.8 V vs. Li+/Li and 147 mAh/g theoretical capacity. LNMO is categorized into the spinel structures with oxygen vacancies. There is two crystal symmetry for synthetic LNMO including Fd3̅m and P4332, corresponding to disordered and ordered Ni/Mn location in octahedral sites, respectively. The Jahn-Teller distortions for oxygen deficiency cause to the formation of M3+ during delithiation and improvement electrochemical behavior. So, the Mn3+/Mn4+ redox couple presents a voltage plateau at around 4V during charge/discharge process. The stability of the Mn3+/Mn4+ plateau during several cycles is depended to Fd3̅ m disorders in the crystal structure. Moreover, two plateau at around 4.6 and 4.8 V is related to Ni2+/Ni3+ and Ni3+/Ni4+ redox couples [1]. In order to prevent a dissolution of Mn-ion into the electrolyte solution due to higher difference electronegativity of Mn-O bond than Ni-O bond and increase the cycle 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 213 life, charge-barrier dopants and surface modification are two important solution, which is mostly reported. In 2017, Giulio Gabrielli had synthesized LiNi0.5Mn1.5O4 modified by LiNbO3 with 97 and 90 mAh/g specific capacity at 5C-rate before and after modification [2]. Sheng Li has investigated the effect of Na2CO3 and NaHCO3 as a precipitating agent on the electrochemical performance of LNMO. LMNO hollow spheres synthesized by Na2CO3 were shown 128, 121 and 120 mAh/g at 0.1, 5 and 10C, respectively with 80% retention after 100 cycles. Furthermore, the energy densities of as high as about 600 Wh Kg−1 and 520 Wh Kg−1 were obtained at the rates of 0.1 and 5C, respectively, as for power density from 59.7 to 2000 W Kg−1 with the increase of current density from 0.1 to 5C [3]. In addition, Metal-doping into the L1-x-y (NiMn)x My O4 with y=0.1-0.2 was frequently reported [1, 4, 5]. Recently, the scientists could synthesize modified-LNMO with 135 mAh/g specific capacity at 1C, which can remain to 105 mAh/g at 30C discharge rate after 1200 cycle.