| The development of high-safety and low-cost aqueous ion batteries is of significance in the background of carbon neutrality.However,aqueous batteries usually suffer from low capacity and poor cycling stability,thus restricting their massive deployment in practice.Due to the unique redox characteristics of Cu2+,as both carrier and redox center,Cu-ion batteries have the potential of high capacity.In this thesis,the following works are carried out,focusing on the electrode materials and systems of aqueous copper ion batteries.(1)First,we examined Cu ion storage in Se,which is highly conductive and electrochemically activite towards Cu2+.Se can deliver a specific capacity of 662 mAh g-1 at 0.5 A g-1,and 604 mAh g-1 at a much higher current of 10 A g-1.The capacity retention is 82%over 2000 cycles at 10 A g-1.Combining in-situ and ex-situ tests,the charge storage mechanism of Cu ions in Se was analyzed as a two-step reaction.The first step involves the irreversible conversion of Se to CuSe,and the second step involves the reversible transition from CuSe to Cu2Se.During the transition,the formation of some CuxSe intermediates can also be confirmed.In addition,we constructed Zn//Se hybrid ion batteries,which exhibit energy and power densities of 337 Wh kg-1 and 484 W kg-1 on the basis of active materials.(2)Then,we designed SexS1-x solid solution to take advantage of high capcity of S and high conductivity of Se.Specifically,Se0.25S0.75 affords a higher capacity of 1276 mAh g-1,a rate capacity of 1082 mAh g-1 at 5 A g-1,and sustains more than 1000 cycles at a high rate of 5 A g-1.In-situ and ex-situ tests were used to probe the charge storage mechanism of the Se0.25S0.75.The first step involves the irreversible conversion of Se0.25S0.75 to CuS and CuSe,and the second step involves the reversible transition Cu2Se+Cu2S?CuSe0.25S0.75.Again,intermediate phases such as CuSe,Cu7S4,Cu1.8Se can be identified.The Zn//Se0.25S0.75 hybrid battery exhibits high energy and power densities of 465 Wh kg-1 and 387 W kg-1,respectively.(3)Moreover,we explored CuS nanosheet arrays to taking profit of high conductivity and 3D architecture.Electrochemical results reveal a high capacity of 510 mAh g-1,robust rate capability of 497 mAh g-1 at a high rate of 7.5 A g-1,and ultrastable cycling by retaining 91%of the initial capacity over 2500 cycles.The charge-storage mechanism was systematically investigated by ex-situ and in-situ techniques,involving a reversible transition from CuS to Cu7S4 and to Cu2S through the redox of Cu2+/Cu+.The constructing Zn//CuS hybrid battery affords cell-level energy and power of 286 Wh kg-1 and 900 W kg-1,respectively.(4)Finally,we developed CuSe nanosheet arrays with fast ion diffusion and high electrical conductivity.Such CuSe electrode enables a vigorous electrochemical performance,exhibiting a reversible capacity of 344 mAh g-1,a rate capability of 285 mAh g-1 at 20 A g-1,and remarkable durability up to 30000 cycles.Charge storage mechanism of CuSe has been explored by in-situ and operando techniques,which reveal a reversible transformation from CuSe to Cu2Se through the intermediates of Cu3Se2 and Cu1.8Se.Furthermore,a co-insertion strategy of Cu2+ and H+ has been proposed to facilitate this transition and to increase the capacity.Pairing CuSe with Zn leads to hybrid aqueous cells,which afford a specific energy and power of 190 Wh kg-1 and 1366 W kg-1,respectively.This work offers an insight into the design of battery systems based on unconventional redox of charge carriers and would have a profound impact on the innovation of energy storage chemistries and technologies. |
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