Two Methods For Improving The Electrochemical Performance Of Aqueous Ion Batteries And Related Mechanisms

With the rapid development of clean energy around the world,it brings great challenges to energy storage and conversion systems.Aqueous ion batteries have greater application prospects in large-scale energy storage in the future due to their high safety,environmental friendliness,low cost,and high ionic conductivity.However,the application of aqueous electrolytes is limited due to the narrow electrochemical stability window of water,and the development of aqueous ion batteries still faces challenges in terms of energy density and cycling stability.It is crucial to develop a low-cost and environmentally friendly electrolyte that can both suppress water reactivity and improve ionic conductivity.In the first part of this thesis,an aqueous electrolyte based on Li₂SO₄–Na₂SO₄–sodium dodecyl sulfate（LN-SDS）was designed,where（1）Na⁺ions dissociated from SDS increase the charge carrier concentration;（2）DS^?/SO₄^2?anions and Li⁺/Na⁺cations are capable of trapping water molecules through hydrogen bonding and hydration,resulting in water reactivity;（3）Li⁺ions reduce the Krafft temperature of LN-SDS,facilitating declined electrolyte melting point;（4）Na⁺and SO₄^2?ions increase the low-temperature electrolyte ionic conductivity;and（5）SDS micelle clusters are orderly aggregated to form directional ion transport channels,enabling formation of quasi continuous ion flows without（r.t.）and with（≤0°C）applying voltage.The screened LN-SDS is featured with suppressed water reactivity and high ionic conductivity at temperatures ranging from room temperature to?15°C,it exhibits ionic conductivities of 41–93 m S cm^–1 at room temperature and 12.6–16.9 m S cm^–1 at?15°C,which are higher than those of conventional water-in-salt electrolytes.Also,Na Ti₂（PO₄）₃‖Li Mn₂O₄ batteries operating with LN-SDS manifest impressive electrochemical performance at room temperature,low-temperature（?15°C）,and high-temperature（50°C）,especially the cycling stability and low-temperature performance.At room temperature,the discharge specific capacity of Na Ti₂（PO₄）₃‖Li Mn₂O₄ battery operated with LN-SDS-90 electrolyte after 2000 cycles at different rates remained at 47.1 m A h g^?1,and the capacity retention rate was 70.4%;After 2000 cycles at 5 C,the discharge specific capacity of 30.8 m A h g^?1is retained,with a capacity retention rate of 76.8%and a coulombic efficiency close to 100%.Even after1000 cycles at?15°C at different rates,the discharge specific capacity remains at 10.7m A h g^?1,exhibiting nearly 100%Coulombic efficiency and 71.3%capacity retention.Electrode materials are one of the key components of aqueous ion batteries,which determine the working voltage and cycle life of aqueous ion batteries.Therefore,choosing a suitable electrode material is crucial to the cycling stability of the battery.In the second part of this thesis,Na⁺/K⁺-co-doped nanoscale amorphous manganese oxide（NKAMO）was synthesized for the first time by one-pot method of atmospheric hydrothermal reaction,K⁺-doped amorphous manganese oxide（NKAMO）and Na⁺-doped amorphous manganese oxide（NAMO）were synthesized by the same preparation method.The electrochemical properties of the as-synthesized amorphous manganese oxides were comparatively investigated with commercially available battery grade manganese dioxide and carbon package detached from commercial alkaline Zn-Mn dry batteries.The results show that the NKAMO electrode exhibits superior specific capacity and the best cycling performance,maintaining a specific capacity of 41.3 m A h g^?1 even after 1000 cycles.Then,using the prepared NKAMO as the positive electrode material and Na Ti₂（PO₄）₃ as the negative electrode material,the NKAMO‖Na Ti₂（PO₄）₃ aqueous sodium-ion battery was assembled.The battery has a specific discharge capacity of 42.5m A h g^?1 after 1000 cycles at a rate of 1 C,with a high capacity retention rate of 85%.And after 5000 cycles at different rates,the discharge specific capacity can still be maintained at 33.2 m A h g^?1,and the capacity retention rate is 66.4%.The battery was continuously charged and discharged for 2800 times at a high rate of 5 C,the battery still retained a specific discharge capacity of 26.1 m A h g^?1,the capacity retention rate was as high as 80.3%,and there was no obvious structural change in the electrode material.