Studies On Novel Aqueous Alkali Ion Batteries

Aqueous alkali metal ion batteries are promising candidates for grid-scale energy storage owing to the safety,non-toxicity and low cost.Considering that the abundances of sodium and potassium in the earth's crust are much higher than that of lithium,aqueous Na⁺/K⁺-ion batteries are more attractive in view of the low cost.This thesis focuses on aqueous Na⁺/K⁺-ion batteries and report the following three works:First,the Water-in-Salt?Wi S?electrolytes are a class of aqueous solutions with high salt concentration,which can effectively widen the electrochemical window of aqueous electrolytes.However,there is no an idea Na-based Wi S electrolyte so far,has been reported till now,limiting the energy density of aqueous Na-ion battery.Here,we dissolve the tetraethylammonium triflate?TEAOTF?salt with organic large radius cation and the sodium triflate?Na OTF?salt in water to design a new class of inert-cation assisted Water-in-Salt?IC-Wi S?electrolyte,which not only realizes a total concentration of 31 m?9 m Na OTF+22 m TEAOTF?,but also possesses low viscosity?30.2 m Pa·s at 25^oC?and high conductivity?11.2 m S/cm at 25^oC?.With the assist of Raman,nuclear magnetic resonance?NMR?measurements and molecular dynamics?MD?simulations,we reveal the cation-anion and salt-water interactions in the IC-Wi S electrolyte.Meanwhile,the IC-Wi S electrolyte possesses many advantages such as,inhibiting the hydrogen evolution owing to a wide electrochemical window,avoiding the cation co-intercalation issue in the mixed alkali ion electrolytes due to the inertness of the large radius TEA⁺cation to electrodes,mitigating dissolution of the electrodes due to a reduced free water and so on.Moreover,the Na_1.88Mn?Fe?CN?₆?_0.97·1.35H₂O//Na Ti OPO₄full battery assembled by the IC-Wi S electrolyte can exhibit average voltage of 1.74 V,energy density of 71Wh/kg,as well as lifespan of over 800 cycles at 1C.Based on the 9 m Na OTF+22 m TEAOTF electrolyte,the Na Mn HCF//Na Ti₂?PO₄?₃has been studied,which could realize a high energy density of 87 Wh/kg.Second,aqueous K-ion full batteries?AKIBs?have not been reported yet owing to the limited available electrodes and electrolytes.Here we designed an AKIB fabricated with an Fe-substituted Mn-rich Prussian blue analogue?PBA?K_xFe_yMn_1-y[Fe?CN?₆]_w·z H₂O cathode,an organic 3,4,9,10-perylenetetracarboxylic diimide?PTCDI?anode,and a 22 m KCF₃SO₃Water-in-Salt electrolyte.The optimal PBA cathode K_1.85Fe_0.33Mn_0.67[Fe?CN?₆]_0.98·0.77H₂O possesses a high capacity of 135m Ah/g and superior rate capability with 70%retention at 100C as well as long cycling life of over 10,000 cycles.Based on the results of the Ex situ XRD,X-ray absorption near edge structure?XANES?and first-principles calculations,Fe substitution not only would change the characteristic of Mn²⁺/Mn³⁺-N,inhibit the phase transition of Cubic phase to Tetragonal phase,but also can improve the K⁺-ion and electronic conductivities.In addition,the PTCDI anode shows a high capacity of 125 m Ah/g,and the 22 m KCF₃SO₃electrolyte exhibits a wide window of 3 V,high ionic conductivity?76 m S/cm at 25 ^oC,10 m S/cm at-20 ^oC?as well as characteristic of inhibiting the dissolution of electrodes.Benefiting from the synergistic effect of cathode,anode and electrolyte,the AKIB not only delivers a high energy of 80 Wh/kg,but also remains a high capacity?85%of capacity at 0.5C?at 20C.Moreover,it exhibits long lifespan with 73%retention after 2000 cycles at 4C.Furthermore,we assembled a AKIB pouch cell with 11 m Ah capacity,which can operate well at rates of 0.1-20C and over a wide temperature range?-20-60 ^oC?.Furthermore,we assembled an aqueous K-ion full battery based on a Cu-substituted Mn-rich PBA cathode and an organic PNTCDA anode,delivering a high energy densiy of 102Wh/kg.Third,low-temperature battery technologies have been paid extensive attentions recently.However,most of batteries exhibit poor performance at ultralow temperature due to the low ionic conductivity of electrolytes and poor diffusion dynamic of electrodes?especially,intercalation-type electrodes?.Here,inspired by the recipe of motor vehicle antifreeze fluid:The solution can keep liquid state at lower temperature by introduce certain ratio ethylene glycol to water.We designed a kind of Na antifreeze-based electrolyte:the water and glycol as the solvent,the sodium trifluoromesylate?Na CF₃SO₃?as the salt.The electrolyte possesses acceptable ionic conductivity at various temperatures?27 m S/cm at 25^oC,4.2 m S/cm at-20^oC,0.78m S/cm at-40 ^oC,0.05 m S/cm at-60 ^oC?,enabling the intercalation-type PBA Na_1.65Fe_0.21Mn_0.79[Fe?CN?₆)]_0.92·2.08H₂O cathode and Na Ti₂?PO₄?₃anode be charging and discharging at-60 ^oC.The ¹H NMR tests have been performed to study the hydrogen bond interactions in the antifreeze-based electrolyte,which should account for a wider temperature range of liquid state.Moreover,the full battery exhibits an average voltage of 1.42 V and an energy density of 80 Wh/kg.Furthermore,the antifreeze-based electrolyte could effectively reduce the dissolution of PBA Na_1.65Fe_0.21Mn_0.79[Fe?CN?₆)]_0.92·2.08H₂O cathode during cycling,which helps the full battery to realize a lifespan of over 5,000 cycles.