The Exploration And Investigation On The Electrode Materials For Lithium Ion Batteries

The urgency for energy renewal requires the use of clean energy sources at a higher level than that presently in force due to the depletion of non-renewable resources. Accordingly, investment for the exploitation of renewable energy resources are increasing worldwide, with particular attention to wind and solar power energy plants. The intermittence of these resources requires high efficiency energy storage systems. Lithium ion batteries has the highest energy density among the secondary batteries, which is a highly promising method of the energy storage for the grid operator. So far, the low capacity of cathode material for lithium ion batteries has restricted the enhancement of the overall energy density of lithium ion batteries, which arouses new high capacity cathode material. The spinel Li4Ti5O12, as a zero strain material during the lithium insertion and extraction, exhibits excellent rate and cycling performance. However Li4Ti5O12suffers the problem of "gas-release" during the storage and discharge/charge process, which blocks its industrialization.The following two parts are mainly discussed in this thesis:(1) the synthesis of new cathode material Li6ZnO4, and investigation on its structure stability and electrochemical performance.(2) the effects of electrolyte additive of ethylene sulfite on the formation of SEI (solid electrolyte interface) film on the surface of Li4Ti5O12, and on the rate and cycling performance of Li4Ti5O12, as well as the analysis of the morphology and composition of the SEI film.In this thesis, the phase-pure microsized Li6ZnO4was synthesized using solid-state reaction from the starting materials, U2O and ZnO. A mixture of Li2O (5%excess) and ZnO was pressed into pellets and then heated at500℃in Oxygen atmosphere for10hours. LigZnO4is not stable in the air, and reacts with H2O and CO2in the air slowly, producing Li2CO3and LiOH on the surface. The variable temperature XRD and TG-DSC-MS results show that the crystal transformation of Li6ZnO4occurs at700℃. The Li6ZnO4electrode mixed with conductive additive KB, dilivers a relatively high charge capacity with a lower voltage plateau at1st cycle, which exhibits better dynamic performance than those mixed with conductive additive AB. However, the material cann’t be discharged(the lithium cann’t be inserted) after charged, which is irreversible。The conductive additive KB is not fit for the high potential materials, which might be ascribed to the side reaction between KB and electrolyte above4.5V.In order to explore the SEI formation on Li4Ti5O12surface, different quantities of ethylene sulfite (ES) as additive were added to the electrolyte-1M LiPF6/EC:DMC (1:1). Li4Ti5O12electrode shows an increasing discharge capacity with the increasing ES content in electrolyte at a voltage plateau of1.55V in the1st cycle, which might be caused by the reductive decomposition of additive ES in the electrolyte, and corresponds to the SEI formation on the surface of Li4Ti5O12. However, the SEI film produced during the discharge process of1st cycle is not stable, which will be oxidized during the charge process. Fourier transform infrared spectrum tests show that the SEI film may contain Li2CO3、ROCO2Li、Li2SO3and so on.