Nanosized Materials for High-Rate Lithium-Ion Batteries: Li(Nil/3Mnl/3Col/3)02

摘要

Lithium-ion batteries (LIBs) are widely used in smart grids, energy storage supplies, electric vehicles, etc. The latter application requires high specific power (great charge/discharge rates), so as to ensure the starting acceleration of a vehicle. Practice of electromotive industry and environmental concerns have lead to the quite harsh selection of electrode materials employed in electric and hybrid cars. Toxic LiCoO2 widely used in first commercial LIBs is now shifted by more environmentally benign Li(Ni[x]Co[1-x])O[2], Li(Ni[x]Co[y]A1[1-x-y])O[2], Li(Ni[x]Mn[y]Co[l-x-y])O[2], and LiMn[2]0[4]. All these materials are synthesized commercially by means of by means of traditional technologies (sintering and precipitation). On the other hand, much attention is paid to obtaining electrode materials in a nanosized form. The power density of any battery is significantly governed by the diffusion of lithium ions into/from (and within) the grains of electrode material [1]. Subdivision leads to great increasing in the area of contact between electrode and electrolyte and to decreasing of distances passed by electrons and lithium ions upon diffusion in the electrode material. This means that obtaining electrode materials in a nanosized form may allow for attaining greater charge/discharge rates than in the case of the electrode materials of a large particle size. In our previous works [2-6] partly reviewed in Ref. [7], a modified citric acid aided route has been employed, and nanosized spinel-type materials including LiMn[2]O[4], LiNi[0.5]Mn[1.5]O[4], a gradient material containing a LiMn[2]O[4] core and LiNi[0.5]Mn[1.5]O[4] shell, and Li[4]Ti[5]O[12] have been synthesized. Analysis presented in Refs [2-7] demonstrates that all these materials overwhelm existing commercial samples being able to sustain much greater current loads (up to 65C) without losing their electrochemical activity. In this presentation, our efforts directed towards citric acid aided synthesis of materials of Li(Ni[x]Mn[y]Co[l-x-y])O[2] type are described. In particular, for Li(Ni[l/3]Mn[l/3]Co[l/3])O[2], DTA, surface area and porosity, XRD, SEM/TEM and EXAFS data are obtained, and impedance, galvanostatic and CVA studies are performed. High-rate electrochemical tests are compared with existing data, and some disadvantages of nanosized materials are put forward. It is stressed that a key role in attaining high-rate properties plays the perfectness of materials obtained. Further, nanosized samples have high reaction ability and, unlike their bulk counterparts, do not tolerate even small overdischarges possibly occurring in cases if a failure happens in a battery equalizing control scheme.