Investigation Of Synthesis And Electrochemical Properties Of Li₁₀GeP₂S₁₂ All-solid-state Batteries

With the wide range of application of lithium-ion batteries in the field of portable electronic devices and electric vehicles,the safety performance and energy density of liquid lithium-ion batteries based on organic electrolytes can not meet the current market needs.Therefore,the adoption of non-flammable inorganic solid electrolytes to replace flammable organic electrolytes becomes an effective way to solve this dilemma.For all-solid-state lithium-ion batteries（ASSLBs）,the mismatched electrolyte-electrode interface could lead to the formation of unstable mesophases,resulting in a large charge transfer resistance,and affecting the normal use of the cells.In this paper,Li₁₀Ge P₂S₁₂（LGPS）was synthesized and combined with surface-modified cathode to solve the problem of incompatibility between sulfide electrolyte and transition metal oxide cathodes;The surface of Li anode was modified to solve the problem of interface reaction between LGPS and Li.LCO@LTO/LGPS/Li,NCA@LNO/LGPS/Li and NCA/LGPS/Li（M）cells were assembled.The electrochemical performance of those cells was characterized.The specific conclusions are as follows:（1）The LGPS was successfully synthesized by combination of ball milling and sintering.The ion conductivity of LGPS is 0.252 m S cm^-1 at room temperature（RT）and the activation energy of LGPS is 28.49 k J mol^-1.Through sol-gel method,the surface of Li Co O₂ was covered with a layer of Li₄Ti₅O₁₂;The surface of Li Ni_0.8Co_0.15Al_0.05O₂ was covered with a layer of Li Nb O₃.A layer of SEI protective layer was successfully formed on the surface of Li anode.（2）The first discharge capacity and 30^th cycle capacity of LCO@LTO/LGPS/Li battery are 142.63 m Ah g-1,95.23 m Ah g^-1 respectively,and the capacity retention rate is 66.7%;The first discharge capacity and 30^th cycle capacity of NCA@LNO/LGPS/Li battery are 164.34 m Ah g^-1,109.09 m Ah g^-1 respectively,and the capacity retention rate is 66.38%.In addition,the first-cycle capacity of NCA@LNO/LGPS/Li cells are 104.58 m Ah g^-1,142.10 m Ah g^-1,164.34 m Ah g^-1 and186.90 m Ah g^-1 respectively at RT,45℃,60℃and 80℃.The discharge capacity and coulombic efficiency increase when the temperature increases.The battery shows the best cycling performance at 60℃.（3）The EIS of the two kinds of ASSLBs during the first charging and discharging process,shows that the typical Nyquist diagram of the cell consists of three parts,namely,a semicircle in the high frequency area（HFS）,a semicircle in the middle frequency area（MFS）and a diagonal line in the low frequency area（LFL）.The HFS is attributed to the interface impedance between the electrode and electrolyte,the MFS belongs to the charge transfer process,and the LFL is assigned to the solid-state diffusion process of Li⁺in the electrode material.During the first charging and discharging process,the destruction of the coating with the stress existing in the electrode material,leads to the direct contact between the electrode and electrolyte with formation of the space-charge layer.thus,the electrode/electrolyte interface impedance(R_if)of cells increased;for NCA@LCO/LGPS/Li cells,the R_if and charge transfer resistance(R_ct)decrease when the temperature increases from RT to 80℃.（4）Li（M6）/LGPS/Li（M6）cell was assembled with a layer of SEI film on the surface of Li anode.The polarization voltage of cell keeps unchanged at a constant current cycle for 500 h at 0.1 m A cm^-2;The XRD analysis of the interfacial reactant on Li/LGPS interface,shows that the interfacial reactants Li₂S,Li₃P and Li-Ge alloy were reduced,indicating that the modified Li anode can reduced Li/LGPS interface reaction.The first discharge capacity and 50^th cycle capacity of NCA/LGPS/Li（M0）battery are 116.61 m Ah g^-1,8.8 m Ah g^-1 respectively,and the capacity retention rate is7.5%;The first discharge capacity and 50^th cycle capacity of NCA/LGPS/Li（M6）battery are 136.36 m Ah g^-1,67.43 m Ah g^-1 respectively,the capacity retention rate is49.45%.The modified Li anode is beneficial to the electrochemical performance of the battery.In this paper,there are 73 pictures,7 tables and 129 reference articles.