Research On Life Fading Mechanism Of Li₄Ti₅O₁₂-based Lithium Ion Battery

Li4Ti5O12(LTO)based lithium ion batteries(LIBs)has long been considered as the spokesman of super-long lifetime,fast-charging and excellent safety.However,there are still some key issues that need to be settled or emphasized before their commercialization,including gassing issue and life fading problems.Investigations on the key factors of life fading of LTO battery will play a significant role for improving the electrochemical performance of LTO-based LIBs and further broadening their applications in the theoretical and practical way.On the gassing remedy,we proposed a controllable in-situ passivation film formation method by taking advantage of the intrinsic interfacial interactions between LTO and electrolyte.An optimum range of SOC(State of Charge)for effective passivation film formation was established through adjusting the amont and distribution of active sites.The proposed in-situ formation method can achieve an excellent cycle performance for LTO-based LIBs for the the uniform and full coverage of the formed passivation film.Such a method is more cost-effective than other gas-inhibiting methods,providing a theoretical support for the optimization of formation method and improvement of formation efficiency.The influence of different cathodes on the lifetime of LTO-based LIBs was investigated.The exact destroying mechanism of dissolved manganese ions on the stability of the formed passivation film on LTO anode was specified,by comparing the performance of LiCoO2/LTO and LiMn2O4/LTO,as well as analyzing the influence of the dissolved manganese ions.The investigation provides a foundation for developing new LTO-based LIBs with high capacity manganese oxides.The influence of Li+ transfer dynamics on the cycle performance of high energy LTO-based LIBs with thicker electrode was further investigated.The Li+intercalation/deintercalation process of electrodes and the mass transfer dynamics were analyzed through symmetric cells,three electrode cells and electrochemical impedance spectroscopy.Compared with cells assembled with thin electrode,cells with the same configuring system but thick electrodes exhibited extremely unsatisfactory room-temperature cycle performance and deteriorated more severe with increasing rates.The rate determining step is the delithiation process of cathode.The poor lithium ions(Li+)diffusion and penetrating rate is the main restriction.Further optimization results indicated that,on the premise of reaching the required demands of energy density,increasing the usage of carbon additives which posses large BET surface area in cathode and increasing the conductivity of electrolyte could be benefial for increasing the cycle performance of the high energy LTO-based full cells with thick electrodes.The long-term cycling fading mechanism of 8Ah LTO-based LIBs was specified.The LTO-based LIBs exhibited two distinct kinds of declining trends,which were decreased steady initial and then accelerated in the end.Analysis indicated that the intial sluggish degradation was mainly thermodynamics fading.The following accelerated degradation was a result of both irreversible thermodynamics fading and reversible dynamic fading.The dynamic fading was dominant and mainly caused by the generated gases.Improving the stability of the formed passivation film during high temperature cycling is crucial for the life perponnence of LTO-based LIBs.These results will provide technical supports for understanding the evolution rules of electrochemical performance of LTO-based LIBs.