The Operating Mechanism And Performance Optimization Of Al-Te Batteries

As our country proposes to achieve the targets of "carbon neutralization" and"carbon peaking",energy storage technologies based on chemical batteries have become more important.Therefore,higher requirements are put forward for the development of battery systems with high energy density and long cycle life,and also for the sustainable application of resources.Recently,the novelty secondary multi-ion battery system,metal aluminum-based battery,has attracted much attention due to its favorable energy-to-price ratios,high energy density of aluminum and safety feature,and has potential applications in large-scale energy storage technology.So far,graphite-based carbon materials still have obvious competitive advantages in terms of cycle stability and discharge voltage.However,it is still challenging to meet the demands of next-generation energy storage due to the lower energy density.Chalcogenide elements,including S,Se,and Te,are promising positive electrode material due to their higher energy density and considerable discharge voltage.Among them,Te has a high electrical conductivity,discharge specific capacity of 1260 mA h g-1,and high discharge voltage of 1.5 V,and therefore exhibiting obvious competitive advantages.Currently,the research on Al-Te batteries have not drawn widely attention,and its operating mechanism and critical issues are still not clear.Therefore,the thesis is dedicated to further improving and optimizing the Al-Te battery system.It is found that the Al-Te battery still suffering some critical problems,such as unclear operation mechanism,chemical and electrochemical dissolution of Te positive electrodes,precipitation of soluble Te compounds on the surface of metal aluminum negative electrodes,low utilization of active materials,and poor overall battery performance.To solve these critical issues above-mentioned,the thesis proposes a physical and chemical confinement positive electrode optimization strategy,an interface chemical control negative electrode optimization strategy,and a physical barrier separator optimization strategy,which significantly improves the overall performance of the Al-Te battery.Meanwhile,it provides an important guiding significance for the further optimization of subsequent Al-Te battery devices.The obtained research results and progress as following:(1)A prototype of Al-Te battery was assembled employing TeNWs positive electrode,aluminum foil negative electrode and AlCl3-[EMIm]Cl Lewis acidic ionic liquid electrolyte.It is found that Te positive electrode delivered a theoretical discharge specific capacity of～1260 mA h g-1 and a high discharge voltage of 1.5 V in an aluminum battery system.However,the severe chemical and electrochemical dissolution of Te in acidic electrolytes resulted in rapid capacity decay and poor cycle stability.Additionally,the chemical precipitation of soluble Te compounds on the negative electrode side lead to severe corrosion of the A1 negative electrode and large deposition/stripping overpotential.The clarity of the operation mechanism and the presentation of key issues provide a theoretical basis for the further optimization of the subsequent Al-Te battery.(2)In order to improve the chemical and electrochemical dissolution of Te positive electrode,N-PC-Te composite electrode is fabricated using nitrogendoped porous carbon(N-PC)as Te carrier,aiming to improve the utilization of active materials through physical and chemical confinement.Theoretical calculations reveal the C-Co-N structure exhibiting good catalysis and adsorption characteristics for multi-Te compounds,and the discharge capacity has been significantly improved.However,N-PC carrier suffers obvious volume expansion during the cycling process,resulting in carrier failure.Therefore,rGO is introduced to form a more stable N-PC-rGO-Te electrode and the specific discharge capacity can reach to 909.5 mA h g-1 at current density of 500 mA g-1.Through physical and chemical limited design strategies,it provides effective design routes for the development of other high-energy battery systems.(3)In order to improve the cycle ability of the negative electrode and suppress the chemical precipitation behavior of elemental Te at the metal Al interface,a～5 μm thick protective layer is constructed on the A1 surface using electrochemical inert TiB2 by a blade coating approach,and Al/TiB2 modified negative electrode was formed.It is found that the TiB2 layer can effectively regulate the uniform nucleation and growth of the metal Al interface,promote the uniform deposition/stripping process of Al,and effectively reduce the overpotential.In addition,the soluble multi-Te compounds can be converted on the TiB2 layer through the formation of the Te-O bond,thereby effectively improving its precipitation behavior at the metal A1 interface and ensuring the stability of the negative electrode.The interface chemical regulation strategy of constructing a multifunctional modified layer on the surface of the metal negative electrode provides a design route for the protection of metal electrodes in other battery systems.(4)In order to establish an Al-Te battery system with a more stable cycle and a higher capacity,the separator was modified with acetylene black to form a porous carbon-based modified separator(AB-PVDF-MS).Subsequently,the Al|AB-PVDF-MS|Te battery was assembled using bare Al negative electrode,pure Te positive electrode,and AB-PVDF-MS separator.The inhibitory effect of the modified separator on soluble Te compounds was evaluated.It is found that the highly conductive porous carbon layer promotes the further conversion of soluble Te compounds on the positive electrode,and meanwhile effectively inhibits its diffusion to the negative electrode side.As a result,the discharge specific capacity reaches 1120 mA h g-1 at the current density of 500 mA g-1,providing a solution for greatly improving the utilization of active materials.(5)The performance of the Al-Te battery has been significantly improved through the optimization process of each component of the positive electrode,negative electrode,and separator.In order to obtain the best comprehensive electrochemical performance of the Al-Te battery,the optimization steps are integrated.As a result,the cycle ability and discharge capacity of the integrated Al-Te battery have been further improved.The initial discharge capacity is increased from～400 mA h g-1 to～1130 mA h g-1,and the effective cycle life is increased from 100 to 500 cycles.After 500 cycles,the discharge capacity is still maintained above～414 mA h g-1,and the coulombic efficiency is maintained at～95%,providing new opportunities for building high-energy-density battery systems.