Research On Carbon Tolerance Of The Anode For The Solid Oxide Fuel Cells And On The Solid State Lithium Batteries

Solid-state batteries show higher security than liquid ones,and they are easy to transport,easy to store and have long life,which makes them the development direction of next generation batteries.Solid oxide fuel cells?SOFCs?and all solid state lithium ion batteries are the most typically solid state cells for the primary batteries and secondary batteries,respectively.For SOFCs,hydrogen is the most commonly used fuel.However issues of transportation and storage difficulties,high cost and potential safety hazard of hydrogen impede the industrial development of fuel cells.Recently researchers turn their attention to methane,because of its abundant resource,convenient storage and low cost.However,traditional SOFCs with a Ni anode have a serious carbon deposition problem in methane gas,leading to a sharp decline in long-term stability.Thus,it is crucial to study the carbon tolerance properties for SOFCs anode.For lithium ion batteries?LIB?,it is particularly necessary to improve the energy and power densities since the LIB cannot meet the demands of humans with the development of society.LiCoO₂,the best developed cathode for LIB,shows structual instability,side reaction with the electrolyte and dissolution of transition metal ions(Co³⁺)at high charging cut-off voltage?>4.3V?.Therefore,it is the research focus to enhance the structural and electrochemical stability of LiCoO₂ at high voltage.What is more,traditional solid state electrolytes inevitably face extrusion and collision during transportation and application.It is important to enhance the resistance to deformation and breakage.Solid state electrolytes show chemical or electrochemical reaction with lithium metal,which prevents the development of all solid state batteries.Therefore,it is necessary to improve the corrosion resistance of the solid state electrolyte to lithium metal.Here we report a new method for improving the tolerance to carbon deposition of the Ni cermet anode in methane by impregnating a small amount of Sn or MgO into the porous Ni cermet anode.Excellent long-term stability of the cell is achieved in humidified CH₄ at 700^oC by addition of 1 wt%Sn to the porous anode.The peak power density of the cell reaches 0.28 Wcm² in humidified CH₄ and the current density decreases only by 28%after the cell is operated under a constant voltage of 0.8 V for230 h at 700 ^oC.The characterization analysis indicates that Sn is enriched and Sn/Ni intermetallics form on the anode surface.Among them,Ni₃Sn exhibits a low catalytic cracking activity and a high catalytic oxidation activity for CH₄.By impregnating 2.5wt%MgO into the porous Ni cermet anode,the cell exhibits a high peak power density of 0.714 Wcm^-2 and the output power of the cell only degraded by 15%for more than330 h operating at 800 ^oC.The outstanding coking tolerance performance of the MgO-modified Ni cermet anode is attributed to the enhanced adsorption properties of H₂O and CO₂ on MgO,revealed by combined density function theory?DFT?calculations and experimental characterization.What is more,the addition of a small amount of Sn or MgO does not compromise the electrochemical performance of the cell in H₂.Structural and electrochemical stability of LiCo O₂ is improved by the surface modification method.Surface modification of LiCoO₂ with the ultrathin film of solid state electrolyte of Li_1.4Al_0.4Ti_1.6?PO₄?₃?LATP?has been realized.The electrolyte layer can not only transfer lithium ion,but also prevent the direct contact between the LiCoO₂particles and the electrolyte effectively and thus to suppress the side reactions of them at high charging voltage.Transmission electron microscopy?TEM?images show that a dense LATP coating layer is covered on the surface of LiCoO₂ uniformly with thickness of 3-20 nm.The cycling performances of the LATP modified LiCoO₂ are evaluated in half-cell with liquid electrolyte at the cut-off potential of 3-4.5V and the cycling stability performance is enhanced and dissolution of the Co³⁺is suppressed compared to the bare LiCoO₂.The all-solid lithium polymer batteries?PEO-based polymer electrolyte?is also prepared.The 0.5 wt%LATP modified LiCoO₂ shows much improved cycle performance with the capacity retention of 92.7%of the initial discharge capacity after 20 cycles.The results demonstrate that the side reaction between PEO and LiCoO₂ can be restrained significantly by the compact ultrathin film of LATP.Solid state electrolyte of Li_1+xAl_xTi_2-x?PO₄?₃?LATP?is modified by an additive of LiPO₂F₂?LPOF?before pressed into a disk.The density,mechanical properties and corrosion resistance to the lithium metal of the LPOF-LATP pellet is enhanced.Although small amount of the additive increases the activation energy of the electrolyte,5%LPOF-LATP exhibits the highes ionic conductivity.