Fabrication And The Applications Of New Li-ion Ceramic Electrolytes

Solid electrolyte plays an important role in lithium-ion batteries,fuel cells,gas sensors,electrochromic devices and other fields.The development of new applications of solid electrolytes and the development of new solid electrolytes to meet the new social needs are of great practical significance.In present thesis,the color change characteristics of the composite lithium ion solid electrolyte Li_1.3Al_0.3Ti_1.7P₃O₁₂/LiMnPO₄ ceramics for pH value are investigated.A new solid electrolyte LiMg₂P₃O₁₀ without variable valence elements is developed to solve the problem of compatibility with lithium metal.The details are described as follows:At first,LATP/LMP composite solid electrolyte ceramics were synthesized by solid state reaction method.The high temperature chemical compatibility was found between LATP and LMP materials.The addition of LMP greatly reduced the sintering temperature of LATP.The composite ceramic electrolyte shows a brighter purple color.It is proved to be a pH sensitive reversible discoloration material.It can have a fast change in color change in the alkaline solution of pH=13 or above,and there is an obvious reverse discoloration in 5 min in pH=1solution.Different cations have different effects on their discoloration,and ceramics have faster response in alkaline solutions containing sodium ions.The mechanism shows that LATP and LMP have redox reaction under alkaline conditions,and the change of valence states in Ti and Mn induces discoloration,and the coexistence of electrode materials and electrolyte materials is a necessary condition to ensure the sensitivity of pH.At the same time,the color change of ceramic samples in weak alkaline solution can be accelerated by electric field.In order to find a new type of lithium ion solid electrolyte without variable valence elements,the study was carried out in the system of Li₂O-x MgO-3P₂O₅（x=2,3,4,6,8）.The local part of phase diagram was constructed and the new phase LiMg₂P₃O₁₀ was obtained.The XRD analysis showed that it was monoclinic structure,space group P21/m.The crystal structure consist of MgO₆ octahedron chain and shared corner PO₄ tetrahedron.The chain is constructed in which lithium ions are located in the channel parallel to the b axis.Through the bond valence mismatch theory,the ion migration channel of LiMg₂P₃O₁₀ as a solid electrolyte is discussed.The results show that lithium ions are expected to migrate along the direction of the b axis and have potential applications on the lithium ion solid electrolyte.In the case of the difficulty to obtain single phase LiMg₂P₃O₁₀ from stoichiometric ceramics and small ionic conductivity,single phase ceramics are synthesized in the non stoichiometric LiMg₂P₃O₁₀ceramics with excess of magnesium.The ceramics of LiMg_2.05P₃O_10.05 have higher ion conductivity(up to 1.04 x 10^-5 S cm^-1)at room temperature.Because there is no variable valence elements in the ceramic,it is expected to be used for all solid lithium batteries.At the same time,cyclic voltammetry shows that at 2 mV s^-1,the area specific capacitance of 0.16m F cm^-2 can be obtained,which is expected to be used in all solid supercapacitors.