Preparation And Alectrochemical Properties Of Oxides Anode For Lithium Ion Batteries

Graphite is commonly used as anode material for commercial lithium ion batteries (LIBs). However, its low theoretical capacity and safety problem cannot meet stringent requirements of next generation high performance LIBs. Therefore, it is urgently demanded to explore alternative anode materials with high specific capacity, good rate capability, long cycle life and high safety. Transition metal oxides are promising anode materials for LIBs, due to their high reversible capacity, rich sources, and simple synthesis process. However, most of transition metal oxides suffer from low electrical conductivity and severe volume changes upon insertion and extraction of lithium ions, which easily cause fast capacity degradation of electrode and thereby hinder their practical application in LIBs.In this work, by rational chemical and structural design, high performance transition metal oxide anode materials were prepared through multiple chemical methods. The preparation parameters and formation mechanism of transition metal oxide composites were studied. The influences of crystal structure, phase composition and particle morphology on electrochemical performance were investigated. The mechanism of enhanced reversible capacity, rate capability and cycling stability were discussed.A core-shell structured MoO3/C composite was synthesized by a facile citric-nitrate method. The presence of carbon can offer good electronic conductivity and prevent the aggregation of MoO3 nanoparticles during charge/discharge process, thus improving the rate capability and structural stability of the electrode. As anode material of LIBs, the MoO3/C material shows high specific capacity, excellent rate capability and good cycle stability. A reversible capacity of 500 mAh g-1 is achieved after 100 cycles.A nanaoscale NiO/Ni composite was prepared via an improved citric-nitrate method. The NiO/Ni composite shows uniform particle distribution with size of 30-40 nm. The highly active nickel nanoparticles can promote the reversible formation and decomposition of gel-like film, thereby contributing extra capacity to the electrode. The in situ generated Ni provides high electrical conductivity for electrode reaction, and thus improves rate capability of electrode. The nanostructure of NiO/Ni composite can shorten lithium ion diffusion distance, and relieve stress generated by volume change of NiO, thus improving the cycling stability of electrode. The as prepared NiO/Ni composite shows high reversible capacity, excellent cycling stability, and superior rate capability, with a specific capacity of ca.800 mAh g-1 maintained at a current density of 0.1 C after 50 cycles. Moreover, the synthesized NiO/Ni composite displays a superior electrochemical performance at high temperature (50℃), with a reversible capacity of 766.9 mAh g’1 for 400 cycles at 2C.Taking the advantages of 1-D growth behavior of MoO3 in nitric acid solution and porous structural characteritics of activated carbon, a nanobelt-type MoO3/C composite was fabricated via hydrothermal reaction. MoO3 nanoparticles and carbon are interdispersed uniformly, forming the composite matrix. The carbon serves as a physical barrier to prevent aggregation of the MoO3 nanoparticles during charge/discharge process, and thereby helps to maintain the structure integrity of the nanobelts. The carbon component also acts as a buffer to relieve the large stress caused by large volume changes upon Li uptake/removal, thus enhancing the structural stability of the electrode. The MoO3/carbon electrode exhibits a high specific capacity (up to 1000 mAh g-1 after 50 cycles at a current density of 0.1 A g-1) and superior rate capability (retaining a discharge capacity of 675 mAh g-1 at a current density of 5 A g-1).A novel,3-D hierarchical MoO2/Ni/C architecture was designed and synthesized by a combination of hydrothermal method and chemical vapor deposition. The nickel nanoparticles are in situ formed and disperse uniformly within flower-like MoO2 particles, which are coated by thin carbon layers. The Ni particle acts as a catalyst during carbon coating process to promote the in situ growth of graphene in the carbon layer. Together, MoO2 and nickel nanoparticles, as well as amorphous carbon and graphene sheets build a 3-D hierarchical robust MoO2/Ni/C structure with a good electronically conductive network and lots of void space. Such a 3-D hierarchical structure combines multiple advantageous features, including an enhanced 3-D electronically conductive network, plenty of tunnels for electrolyte solution penetration, void space for volume change accommodation, and more surface areas for electrode reaction. The manufactured MoO2/Ni/C composite exhibits high reversible capacity, and excellent rate capability of 576 and 463 mAh g-1 at current densities of 100 and 1000 mA g-1, respectively. The excellent cycling performance is recorded with capacity of 445 mAh g-1 maintained at 1000 mA g-1 after 800 cycles. The proposed synthesis process is simple and the design concept can be broadly applied, providing a novel, general approach towards manufacturing of metal oxide-based composites.