Solid State Electrolytes And Solid State Batteries: Fundamentals And Applications

Solid state lithiμm batteries are considered as an important aspect of next generation lithiμm ion batteries.Compared with traditional lithiμm ion batteries that use organic liquid electrolytes,solid-state batteries have higher security due to the use of solid state electrolytes.At the same time,metallic lithiμm and anode materials with lithiμm metal could be directly used as anode,which,therefore,can significantly improve the specific energy of lithiμm batteries.Although solid state lithiμm batteries have many advantages compared to traditional lithiμm ion batteries,the electrochemical performance of current solid state batteries cannot meet the practical needs according to the current developing progress.In addition,the maturity of mass production is not remarkable and the cost is uneconomical.In order to further optimize and improve the electrochemical performance of solid batteries,it is necessary to develop high performance solid electrolytes and additives to modify and enhance the interfacial performance between the electrode and solid electrolyte.At the same time,optimizing battery production process and reducing the cost is also of great importance.For the above issues,the research works carried out in this paper were mainly focused on the ion transport mechanism of Al doped Li_1.5Al_0.5Ge_1.5（PO₄）₃ and LAGP/LATP composite electrolytes,electrochemical characteristics of lithiμm metal deposition and anode prelithiation,preparation and performance testing of solid state batteries and rate performance estimation of lithiμm batteries.The detailed statement of the above works can be as follows:Firstly,spherical particle diffusion model（SPDM）based on the bulk diffusion controlled process and the Fick’s diffusion law was constructed and used to estimate the rate performance of lithiμm batteries.Systematic nμmerical calculations were made based on SPDM and the quantitative relationship of C rate with SOC,particle size,and diffusion coefficient was revealed.To verify the simulation results,experiments were designed by testing the rate performance of lithiμm cobalt oxide,and the obtained results demonstrated highly consistent with the simulated calculations.Secondly,pure phase Al doped LAGP and LATP were synthesized through solid state reaction,a series of composite electrolytes consisted of LAGP and LATP with different weight ratio were designed.XRD and variable temperature AC impedance spectra were carried out to clarify the crystal structure and the ion transport properties of the composite electrolytes.The results indicate that the composite electrolyte with the LATP/LAGP weight ratio of 80:20 achieved the highest bulk conductivity,while the highest grain boundary conductivity appeared at the LATP/LAGP weight ratio of 20:80.All the composite electrolytes have higher total conductivity than the pure LAGP and LATP,which highlights the importance of heterogeneous interface on regulating the ion transport properties.Thirdly,in order to investigate the electrochemical performance,including rate,cycling stability and coulombic efficiency,of metallic lithiμm deposition in liquid electrolyte,a series of cells that use LiCoO₂ as cathode and different anode（including Cu,in situ electrochemical deposition Li-Cu and lithiμm metal with different thickness）were assembled and tested.On the other hand,to validate the practical applicability of prelithiation,electrochemical prelithiation method was adopted to lithiated the graphite.Full cells using the lithiμm cobalt oxide LiCoO₂ as cathode and lithiated graphite as anode were assembled and tested.The results showed that the full cell using lithiated graphite anode has better cycling stability and more stable coulombic efficiency during the cycling compared to the non lithiated graphite.Finally,solid state batteries based on PEO and PMMA polymer electrolytes were designed.The physicochemical properties of the polymer electrolyte membrane and the electrochemical performance of solid-state batteries were tested.Besides,the interfacial impedance characteristic among the PEO/LAGP interface was studied.