Electrochemical Properties Of Lithium-rich Manganese-based Cathode Material/Li₄Ti₅O₁₂

Lithium-rich manganese-based cathode material is cleaner and greener, lower cost. The rawmaterials is more abundant than other cathode materials such as lithium cobalt oxide, whichhaving a high energy density and safety. Lithium titanate anode material has a lower irreversiblecapacity and high initial charge-discharge efficiency, high cycling stability because the structureis stable. Its safty is high, because it offers a operating voltage of approximately1.55V vers usLi, and having a higher voltage relative to the carbon negative electrode when matching cathodematerial, the rate of charge-discharge is faster, which is applicable to the hybrid electric vehiclesand electric vehicles.In this thesis, lithium-rich manganese-baesd (RM-1) as the cathode material, lithium titanate(LTO) as the anode， which is assembled into14500-type cylindrical battery. The cycleperformance at different voltages, high temperature performance, low temperature dischargeperformance and different rates discharge performance are studied. The main contents includethe following:First, cycle performance at different voltages of battery is studied. When the voltage islower than3.1V, the discharge specific capacity before50cycles is increased gradually. Whenthe number of cycles at50times to300times the cycle performance is stabilized. When thevoltage is above3.1V, the discharge specific capacity is increased gradually from the beginningof the first25cycles (decreased significantly after250cycles at3.3V). When the number ofcycles at25times to300times the cycle performance is stabilized.Second, the cycling stability of the batteries at55℃and storage performance at55℃,80℃are investigated respectively. Compared with the room temperature, the discharge specificcapacity of the battery increased4.34%at55℃, and exhibit best cycle stability performance.Batteries storaged after3d and1d at55℃and80℃respectively, the voltage drop(0.16V) ismore obvious, showing obvious flatulence phenomenon. It showed that the reaction in thebattery at80℃is more faster than that55℃.Then, the influence on low temperature performance with different conductive agents,different surface densities and compaction densities and different types of electrolyte arecompared. The SEM of different conductive agents and different cathode compaction densitiesare tested. The exterior appearance of KS-6is scaly and difficult to form a dense conductivebridge. The interfacial reaction performance is poor. Super-P is approximately spherical, Its size is small, having a larger specific surface area, which could coated around the materialuniformly. It showed a better conductivity. Carbon nanotubes (CNTs) is a hollow tubularconductive agent, having an excellent conductivity, which could reduce polarization. Thedistance between particles is shortened with the compacted density increased. The results showthat using CNTs, cathode surf ace density of280g/m2, cathode compaction density of3.0g/cm3and using low-temperature ele ctrolyte exhibit better low temperature performance, the capacityretentions relative to25℃are47.77%,35.86%,35.71%and35.33%, respecttively.Finally, the influence on different discharge rates with the same conductive agent,different cathode surface densities and compaction densities, and different forming conditionsare investigated. The studies show that discharge specific capacity with KS-6+Super-P is higherthan with a single conductive agent KS-6and a single conductive agent Super-P at the samedischarge current, amounting to116mAh/g at1C. The capacity retention rate is more than84.10%at6C. The discharge specific capacity is118.4mAh/g at1C after add CNTs, which ishigher than other conductive agents. The discharge specific capacity is improved significantly athigh temperature and high voltage formed, which having a124mAh/g at1C. But the dischargespecific capacity decline significantly at different discharge currents. The capacity retention rateis lss than70%at6C.