Aqueous electrochemical device and preparation method thereof

Abstract

The present disclosure relates to an aqueous electrochemical device comprising a negative electrode, a positive electrode, a separator, and an aqueous electrolyte having a basic pH wherein the positive electrode is provided with at least one layer of nanoparticles capable of forming a locally hydrated hydrogen ion rich environment at the positive electrode during operation of the device, and / or a capacity ratio between the negative electrode and the positive electrode is less than 1, therefore, oxygen is basically prevented from being generated at the positive electrode. Electrochemical devices find particular uses in large scale energy storage.

Description

[0001] Priority Document

[0002] This application claims priority to Australian Provisional Patent Application No. 2022902227, filed on August 8, 2022, entitled “Aqueous electrochemical device and method for making the same”, the contents of which are hereby incorporated by reference in their entirety. Technical Field

[0003] The present disclosure generally relates to aqueous electrochemical devices and methods of making the same. In particular, the present disclosure relates to aqueous metal ion batteries having alkaline pH aqueous electrolytes and methods of making the same. Background of the Invention

[0005] Energy storage will dramatically change the way the world uses energy. In addition to being more flexible, reliable, and efficient, energy storage is an effective way to smooth the supply of variable forms of renewable energy, such as solar and wind power. The need for large-scale energy storage has grown, and one of the most common forms of large-scale energy storage is batteries. 1 Although batteries based on organic electrolytes show high energy density, which is in principle suitable for large-scale energy storage, they suffer from inherent instability and safety issues due to the use of expensive and highly volatile and flammable organic solvents such as dimethyl carbonate and diethyl carbonate, and chemically unstable and toxic salts such as lithium hexafluorophosphate (LiPF6). 2-7 .

[0006] Aqueous batteries are expected to solve these problems and have shown great potential for large-scale energy storage due to their cost-effectiveness, high ionic conductivity and greatly improved safety. Attempts have been made to use aqueous metal ion batteries, including but not limited to aqueous magnesium ion batteries (AMIBs), aqueous aluminum ion batteries (AAIBs) and aqueous alkali metal ion batteries such as aqueous lithium ion batteries (ALIBs), aqueous potassium ion batteries (AKIBs) and aqueous sodium ion batteries (ASIBs).

[0007] However, aqueous electrolytes are known for their narrow electrochemical stability window (ESW, 1.23 V) due to the occurrence of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which imposes undesirable restrictions on the choice of cathode and anode materials. A recently proposed strategy to expand the ESW is to use highly concentrated "water-in-salt" (WIS) electrolyte solutions. 8 , which paves the way for the development of a series of aqueous high-voltage rechargeable batteries. WIS electrolyte enables a wider voltage window (3.0 V) by forming a solid electrolyte interface (SEI) on the anode and suppressing the hydrogen evolution reaction at the anode. By applying an excess of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Suo et al. 8The electrode-electrolyte interface was constructed to suppress the HER, and a special electrolyte structure that can retard the OER was constructed.

[0008] Some inherent properties of aqueous lithium-ion batteries make them less suitable for large-scale stationary energy storage applications, where safety, cycle life and low cost become more important than energy density. Compared with lithium, sodium may be more suitable for large-scale energy storage in aqueous batteries due to its abundance, low cost and wide distribution. 9 .

[0009] In theory, aqueous sodium-ion batteries (ASIBs) can be fabricated by simply applying the WIS strategy and using excess sodium fluoride salts. However, ideal aqueous sodium batteries cannot be achieved due to the limited solubility of sodium salts as electrolyte components. The concentrations of lithium trifluoromethanesulfonate (LiOTF) and potassium trifluoromethanesulfonate (KOTF) can reach 22 M and 20 M, respectively, at 25 °C, but the concentration of sodium trifluoromethanesulfonate (NaOTF) can only reach 9 M. 10 The large amount of free water generated due to low solubility is not only sensitive to oxidation but also may damage the stability of the slightly water-soluble LiF- or NaF-rich solid electrolyte interface (SEI) in suppressing HER. Recently, some researchers have introduced alternative strategies such as bisalts or other organic compounds to overcome the solubility limitation of sodium salts. 11-13 However, many of these efforts involve the use of expensive fluoride-containing salts and organic compounds, which can pose potential toxicity, corrosiveness, and increased electrolyte costs.

[0010] Others have proposed increasing pH to suppress HER at the anode, but this approach would compromise the stability at the cathode. 14,15 The overall electrochemical stability window of the aqueous electrolyte remains unchanged. The OER is highly sensitive to pH and is more violent under alkaline conditions than under neutral conditions, as shown in the Pourbaix plot. 1 .

[0011] Therefore, there remains a need for aqueous batteries that can solve or alleviate one or more of the above-mentioned problems and can have practical use in large-scale energy storage. Summary of the invention

[0012] In a first aspect, an aqueous electrochemical device is provided, comprising a negative electrode, a positive electrode, a separator and an aqueous electrolyte having an alkaline pH, wherein the positive electrode is provided with at least one layer of nanoparticles capable of forming a local hydronium ion-rich environment at the positive electrode during operation of the device, and / or the capacity ratio between the negative electrode and the positive electrode is less than 1 (i.e., N / P capacity ratio <1) to substantially avoid the generation of oxygen at the positive electrode.

[0013] In a second aspect, a method for manufacturing an aqueous electrochemical device is provided, the aqueous electrochemical device comprising a negative electrode, a positive electrode, a separator and an aqueous electrolyte having an alkaline pH, wherein the method comprises applying at least one layer of nanoparticles on the positive electrode capable of forming a local hydronium ion-rich environment at the positive electrode during operation of the device, and / or making the capacity ratio between the negative electrode and the positive electrode less than 1 (i.e., N / P capacity ratio <1) to substantially avoid the generation of oxygen at the positive electrode.

[0014] In certain embodiments of the first or second aspects, the aqueous electrochemical device is an aqueous battery. In some embodiments, the aqueous battery is an aqueous metal ion battery. In some further embodiments, the aqueous battery is an aqueous lithium ion battery, an aqueous sodium ion battery, or an aqueous potassium ion battery. In some specific embodiments, the aqueous battery is an aqueous sodium ion battery.

[0015] In certain embodiments of the first or second aspects, at least one layer of nanoparticles is made of a support and a metal selected from Ni, Pt, Fe, Co, Pd, Cu, and combinations thereof. In some embodiments, the support is selected from carbon black, carbon nanotubes, graphite, graphitized carbon black, graphene, reduced graphene oxide (rGO), and combinations thereof.

[0016] In some embodiments of the first or second aspects, the nanoparticles are selected from Ni / C, Pt / C, Fe / C, Co / C, Pd / C, Cu / C, PtNi / C, PtFe / C, PtCo / C, PtCu / C, PdNi / C, Ni / rGO, Pt / rGO, Fe / rGO, Co / rGO, Pd / rGO, Cu / rGO, PtNi / rGO and PdNi / rGO nanoparticles. In some embodiments, the nanoparticles are selected from Ni / C, Fe / C, Co / C and Cu / C nanoparticles. In some further embodiments, the nanoparticles are Ni / C and / or Co / C nanoparticles, and their Ni and / or Co loadings are from about 1wt% to about 40wt%. In even further embodiments, the nanoparticles are Ni / C and / or Co / C nanoparticles, and their Ni and / or Co loadings are from about 20wt%.

[0017] In certain embodiments of the first or second aspects, the nanoparticles have an average particle size ranging from about 1 nm to about 100 nm. In some embodiments, the nanoparticles have an average particle size ranging from about 40 nm to about 60 nm.

[0018] In certain embodiments of the first or second aspect, the at least one layer of nanoparticles has a thickness of about 5 μm to about 100 μm.

[0019] In certain embodiments of the first or second aspect, the pH of the aqueous electrolyte is from about 9 to about 13. In some embodiments, the pH of the aqueous electrolyte is from about 12 to about 13.

[0020] In certain embodiments of the first or second aspects, when the aqueous electrochemical device is an aqueous sodium ion battery, the aqueous electrolyte with an alkaline pH comprises a salt as an electrolyte selected from sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium nitrate (NaNO3), sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium acetate (CH3COONa), sodium carbonate (Na2CO3), sodium hexafluorophosphate (NaPF6) and combinations thereof. In some embodiments, the aqueous electrolyte with an alkaline pH is a saturated aqueous solution of sodium perchlorate.

[0021] In certain embodiments of the first or second aspects, when the aqueous electrochemical device is an aqueous sodium ion battery, the positive electrode comprises a positive electrode material selected from the group consisting of: Na x Fe y Mn 1-y [Fe(CN)6] w ·zH2O(1≤x≤2,0.8≤y≤1,0.8≤w≤1,0.5≤z≤2), Na2Mn x Fe 1-x Fe(CN)6(0.8≤x≤1), Na2Mn x Ni 1-x Fe(CN)6(0.8≤x≤1), Na2Mn x Co 1-x Fe(CN)6(0.8≤x≤1.0), Na3V2(PO4)2F3, Na 0.44 MnO2, Na2NiFe(CN)6, Na2CuFe(CN)6, Na2NiMn(CN)6, Na3V2(PO)4, NaMnO2, Na 0.66 [Mn 0.66 Ti 0.34 ]O2, Na2Zn3[Fe(CN)6]2, Na3MnTi(PO4)3 and Na4Fe3(PO4)2(P2O7). In some embodiments, the positive electrode material is Na2MnFe(CN)6 ('NMF').

[0022] In certain embodiments of the first or second aspects, when the aqueous electrochemical device is an aqueous sodium ion battery, the negative electrode comprises a negative electrode material selected from the group consisting of NaTi2(PO4)3('NTP'), Na3MnTi(PO4)3, NaTiOPO4, Na2VTi(PO4)3, Na3V2(PO4)3, TiSe2, TiS2, hard carbon, and perylenetetracarboxylic acid diimide. In some embodiments, the negative electrode material is NaTi2(PO4)3.

[0023] In certain embodiments of the first or second aspects, the capacity ratio between the negative electrode and the positive electrode is about 0.56:1 to about 0.95:1, such as about 0.62:1 and about 0.75: 1. In some embodiments, the capacity ratio between the negative electrode and the positive electrode is about 0.62:1.

[0024] In certain embodiments of the first or second aspects, the aqueous electrochemical device exhibits at least about 90 Wh kg at 0.5C. -1 In some embodiments, the aqueous electrochemical device has a cycle life of more than 14,000 cycles at 10C. In some embodiments, the aqueous electrochemical device has a cycle life of up to 200 cycles at 1C. In some further embodiments, the aqueous electrochemical device exhibits a capacity retention of 86% at 0.5C after 200 cycles at -30°C. -2 In the case of Na2MnFe(CN)6 / NaTi2(PO4)3 soft-pack cells with similar electrode loadings, the aqueous electrochemical device exhibited an average Coulombic efficiency of 99% at 1C and retained 85% of its capacity after 1,000 cycles. -2 In the case of a 50mAh Na2MnFe(CN)6 / NaTi2(PO4)3 soft pack battery, the aqueous electrochemical device was operated at 300mAg at 25°C. -1 After 200 cycles, the capacity retention rate is nearly 100%.

[0025] In a third aspect, a positive electrode for an aqueous electrochemical device is provided, on which at least one layer of nanoparticles capable of forming a local hydronium ion-rich environment at the positive electrode during operation of the device is provided. The nanoparticles, at least one layer of nanoparticles, the positive electrode and the electrochemical device may be those described in the first aspect.

[0026] In a fourth aspect, a method for preparing a positive electrode for an aqueous electrochemical device is provided, wherein the method comprises applying at least one layer of nanoparticles capable of forming a local hydronium-rich environment at the positive electrode during operation of the device on the positive electrode. The nanoparticles, at least one layer of nanoparticles, the positive electrode and the electrochemical device may be those described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Non-limiting embodiments of the present disclosure will be discussed with reference to the accompanying drawings, in which:

[0028] FIG1 shows: (a) X-ray powder diffraction (XRD) spectrum of Ni / C, and (b) transmission electron microscopy (TEM) image of Ni / C (PDF#04-0850).

[0029] Figure 2 The linear sweep voltammetry (LSV) curve after positive electrode surface treatment is shown: Cal: 0.000174 μm / pix; 11:012022-7-27; Camera: NANOSPRT15, ​​Exposure: 400 (ms) × 4 standard frames, Gain: 1, Bin: 1; Gamma: 1.00, no sharpening, normal contrast.

[0030] Figure 3 Depicted are: (a) the discharge capacity of the battery at different rates, and (b) the Coulombic efficiency of the battery at different rates.

[0031] Figure 4 The electrochemical performance of NMF / NTP full cells in the voltage range of 0.5 to 2.2 V is depicted. (a) Rate performance and corresponding Coulombic efficiency of NMF / NTP full cells at different current rates using a local microenvironment (LME) at room temperature. (b) Comparison of average voltages of NMF / NTP full cells at different current rates in different systems at room temperature. (c) Cycling performance of NMF / NTP full cells in different systems at 1C current rate at room temperature. (d) Cycling performance of NMF / NTP full cells in different systems at 0.5C current rate and -30°C. (e) Long-term cycling performance of NMF / NTP full cells at 10C current rate and room temperature using a local environment (cathode mass loading: 20.45 mg cm -2 , anode mass loading: 19.45 mg cm -2 , the ratio of the mass of the negative electrode material contained in the negative electrode to the mass of the positive electrode material contained in the positive electrode is about 0.95:1).

[0032] Figure 5 Depicted are the cycling performance of NMF / NTP full cells at 0.5C: (a) discharge capacity, and (b) Coulombic efficiency.

[0033] Figure 6A comparison of reported sodium-aqueous batteries and batteries according to the present disclosure is shown.

[0034] FIG7 shows a comparison of the cost and electrochemical performance of the battery according to the present disclosure with previously reported batteries. (a) Total cost comparison with reported aqueous Li, Na and K ion full batteries (prices based on Australian sigma, Table 1). (b) Comparison of life and energy density with reported aqueous Na and K ion full batteries. (c) Comparison of the battery according to the present disclosure with commercial batteries, as shown in Table 2.

[0035] Figure 8 Safety testing of ASIB soft-pack batteries using positive surface treatment is shown. (a) Output voltage of the soft-pack battery. (b) Picture of a blue light lamp powered by two ASIB soft-pack batteries. (c) Picture of a soft-pack battery that was cut and immersed in water to power a blue light lamp. (d) Charge and discharge curves of a 32mAh ASIB soft-pack battery. (e) Picture of an electric fan powered by an ASIB soft-pack battery. (f) Charging curves of an ASIB soft-pack battery before and after being cut and immersed in water. (gi) The recharged cut soft-pack battery continuously powered a thermometer and hygrometer in water for more than 10 hours.

[0036] Fig. 9 The generation of the local environment is depicted. (a) In situ surface-enhanced IR spectra of C at different potentials. (b) In situ surface-enhanced IR spectra of Ni / C at different potentials. (c) Operant differential electrochemical mass spectrometry (DEMS) results for evaluating H2 and O2 evolution when NMF / NTP cells are cycled at 0.5C in the voltage range of 0.5 V to 2.2 V. (d) Scanning electron microscope cross-sectional image of Ni / C-coated NMF. (e) Schematic diagram of the water reduction mechanism on pure carbon and Ni / C on the electrode surface in alkaline electrolyte.

[0037] Fig.10 In situ Fourier transform infrared (FTIR) spectroscopy of C and Ni / C in neutral electrolyte is shown.

[0038] Fig.11The exploration of the reaction mechanism and in-situ Ni substitution are shown. (a) Charge-discharge curves of NMF / NTP electrode in neutral electrolyte, (b) Charge-discharge curves of NMF / NTP electrode in alkaline electrolyte, (c) Charge-discharge curves of NMF / NTP electrode in alkaline electrolyte with positive electrode surface treatment strategy, (d) TEM images of NMF electrode after cycling in neutral electrolyte, in alkaline electrolyte, and with positive electrode surface treatment strategy in alkaline electrolyte, (e) Energy dispersive X-ray (EDS) spectra of NMF electrode after cycling in neutral electrolyte, in alkaline electrolyte, and with positive electrode surface treatment strategy in alkaline electrolyte, (f) Raman spectra of NMF electrode after cycling in neutral electrolyte, in alkaline electrolyte, and with positive electrode surface treatment strategy in alkaline electrolyte.

[0039] Fig.12 The electrochemical performance of NMF / NTP full cells in the voltage range of 0.5 to 2.2 V is depicted. (a), (c), and (e) Cycling performance of NMF / NTP full cells with Pd / C, Cu / C, or Co / C nanoparticle layers on the positive electrode at 1C at 25 °C. (b), (d), and (f) Charge / discharge curves of NMF / NTP full cells with Pd / C (b), Cu / C (d), or Co / C (f) nanoparticle layers on the positive electrode.

[0040] Fig.13 The cycling performance of the NMF / NTP full cell with an NTP / NMF ratio of 1:1 and the NMF / NTP full cell with an NTP / NMF ratio of 0.75:1 are depicted.

[0041] Fig.14 The cycling performance of the NMF / NTP full cell with an NTP / NMF ratio of 1:1 and the NMF / NTP full cell with an NTP / NMF ratio of 0.62:1 are depicted.

[0042] Fig.15 The cycling performance of the NMF / NTP full cell with an NTP / NMF ratio of 1:1 and the NMF / NTP full cell with an NTP / NMF ratio of 0.56:1 are depicted. DETAILED DESCRIPTION

[0043] The term "electrochemical device" as used herein refers to a device that can convert chemical energy into electrical energy through an electrochemical reaction.

[0044] The term "aqueous electrolyte" as used herein generally refers to a water-based electrolyte solution. However, this does not exclude the possibility of the presence of a certain amount of organic co-solvents (such as dimethyl carbonate (DMC) and acetonitrile) that do not adversely affect the formation of a local hydronium-rich environment at the positive electrode by means of at least one layer of nanoparticles disposed on the positive electrode.

[0045] The term "water-in-salt electrolyte" as used herein refers to a highly concentrated electrolyte solution in which there are far more dissolved salt molecules than water molecules (salt / solvent ratio > 1, by volume or weight) and there are barely enough water molecules to form a "classical" primary solvation.

[0046] The term "negative electrode material" as used herein refers to an active material of a negative electrode of an electrochemical device. The term "positive electrode material" as used herein refers to an active material of a positive electrode of an electrochemical device.

[0047] As used herein, the phrase "hydrogen-rich" means H3O + Ions accumulate on the cathode surface, which can be detected by in situ IR in H3O + The asymmetric OH stretching mode at 2020 cm -1 and umbrella vibration at 1230cm -1 It should be understood that the hydronium-rich environment at the positive electrode leads to a local acidic environment at the electrode.

[0048] The term "capacity" in relation to an electrode herein refers to the total amount of electricity produced due to an electrochemical reaction at the electrode. It can be determined by the available amount (eg, mass) of the electrode active material that participates in the redox reaction.

[0049] The term "capacity ratio between the negative electrode and the positive electrode" used herein is also well known in the industry and is referred to as N / P capacity ratio.

[0050] The present disclosure is derived from the inventor's research on the stability of aqueous electrochemical devices. It is surprisingly found that during the operation of the device, the formation of a local hydronium ion-rich environment at the positive electrode (cathode) in an alkaline (or high pH) electrolyte can inhibit the production of oxygen at the positive electrode, while the alkalinity of the electrolyte helps to slow down the production of hydrogen at the negative electrode (anode). In this way, the electrochemical stability window (ESW) of the aqueous electrolyte can be expanded and the stability of the aqueous electrochemical device can be improved. For example, when a manganese-rich Prussian blue analog (PBA) such as Na2MnFe(CN)6 is used as a positive electrode material and at least one layer of nickel-based nanoparticles is provided on the positive electrode, the edges of the nickel-based nanoparticles promote the dissociation of water and produce a large amount of H*. However, at a positive potential, H* is difficult to adsorb to the positive electrode surface, but the H ions are still bound to nearby water molecules, rather than to the catalyst surface. Therefore, the hydronium ion (H3O + ) accumulates on the positive electrode surface, forming a local acidic environment. + The environment can effectively prevent OH in the bulk electrolyte - Contact the cathode, thereby inhibiting the OER at the cathode. +The environment can also prevent OH - The adsorption of Ni species to the cathode surface attenuates the dissolution of Mn and stabilizes the cathode. During the charging process, it was found that the oxidation of Ni-based nanoparticles in the layer promotes the 2+ In-situ replacement of Mn further enhances the stability of the aqueous electrochemical device. It was also surprisingly found that making the capacity ratio between the negative electrode and the positive electrode (i.e., the N / P capacity ratio) less than 1 allows the voltage of the electrochemical device to be changed to a voltage range where hydrogen is more likely to be produced and substantially avoids the production of oxygen at the positive electrode. This cathode sacrificial strategy, combined with an alkaline pH (or high pH) electrolyte that helps suppress hydrogen production at the negative electrode, can significantly improve the stability of the aqueous electrochemical device.

[0051] Accordingly, an aqueous electrochemical device is disclosed herein, comprising a negative electrode, a positive electrode, a separator, and an aqueous electrolyte having an alkaline pH. The positive electrode is provided with at least one layer of nanoparticles capable of forming a local hydronium-rich environment at the positive electrode during operation of the device. Additionally or alternatively, the capacity ratio between the negative electrode and the positive electrode is less than 1 to substantially avoid the generation of oxygen at the positive electrode.

[0052] The aqueous electrochemical device disclosed herein may be in the form of a battery or a battery cell. For illustrative purposes, the aqueous battery may include an aqueous magnesium ion battery (AMIB), an aqueous aluminum ion battery (AAIB), and an aqueous alkali metal ion battery, such as an aqueous lithium ion battery (ALIB), an aqueous potassium ion battery (AKIB), and an aqueous sodium ion battery (ASIB). In some embodiments, the aqueous electrochemical device may be an ALIB because they tend to have a high energy density. In some other embodiments, an aqueous sodium ion battery (ASIB) may be more preferred due to the abundance of raw materials, safety, and low cost.

[0053] As mentioned above, the electrochemical stability window of aqueous batteries is narrow to about 1.23 V due to the occurrence of hydrogen production and / or oxygen production reactions, which limits the selection of cathode and anode materials. Ideally, the redox potential of the electrode should be between the hydrogen production potential and the oxygen production potential to avoid water electrolysis.

[0054] Generally, the negative electrode materials and positive electrode materials of aqueous batteries known in the art can be used in the present disclosure. Examples of negative electrode materials for aqueous lithium-ion batteries include conductive additives, LTO (lithium titanate), surface functionalized silicon, and high-performance powdered graphene. Lithium cobalt dioxide LiCoO2, lithium nickel dioxide LiNiO2, lithium manganese dioxide LiMnO2, lithium manganese oxide LiMn2O4, lithium nickel manganese oxide Li 1.0 Ni 0.5 Mn 1.5 O4, Lithium Nickel Manganese Cobalt Oxide LiNi 0.33 Mn0.33 Co 0.33 O2, or high energy lithium nickel manganese cobalt oxide Li 1.2 Ni 0.176 Mn 0.524 Co 0.100 Lithium metal oxide compounds such as O2 can be used as positive electrode materials. FeS2 and lithium iron phosphate can also be considered. If necessary, element doping and coating modification can be applied to modify the electrode material.

[0055] Turning to aqueous sodium ion batteries, the negative electrode material can be selected from NaTi2(PO4)3(NTP), Na3MnTi(PO4)3, NaTiOPO4, Na2VTi(PO4)3, Na3V2(PO4)3, TiSe2, TiS2, hard carbon and perylene tetracarboxylic acid diimide. In some embodiments, the negative electrode material is NaTi2(PO4)3. Among the positive electrode materials that can be used to make the aqueous sodium ion batteries disclosed herein, Prussian blue analogs (PBA) are promising due to their excellent redox properties and relatively high standard potential. For ASIB, PBA can have the general formula Na x P[R(CN)6] 1-y wH2O, where P and R are transition metals such as Mn, Ni, and Fe, and y is the number of [R(CN)6] vacancies. The cage-like structure exhibits broad channels, allowing for the insertion of a variety of intercalation ions. PBAs can be prepared from abundant and non-toxic elements via a simple and low-cost coprecipitation synthesis of metal salts and hexacyanoferrate complexes. In this regard, Na x Fe y Mn 1-y [Fe(CN)6] w ·zH2O(1≤x≤2,0.8≤y≤1,0.8≤w≤1,0.5≤z≤2), Na2NiFe(CN)6, Na2Mn x Fe 1-x Fe(CN)6(0.8≤x≤1) such as Na2MnFe(CN)6(NMF), Na2Mn x Ni 1-x Fe(CN)6 (0.8≤x≤1), Na2Zn3[Fe(CN)6]2, Na2CuFe(CN)6 and / or Na2NiMn(CN)6 as positive electrode materials. Other examples of positive electrode materials that can be used for the aqueous sodium ion battery disclosed herein also include but are not limited to Na 0.44 MnO2, Na3V2(PO)4, NaMnO2, Na 0.66 [Mn 0.66 Ti 0.34]O2, Na3MnTi(PO4)3, Na2Mn x Co 1-x Fe(CN)6(0.8≤x≤1.0), Na3V2(PO4)2F3 and Na4Fe3(PO4)2(P2O7).

[0056] In order to suppress the generation of oxygen at the positive electrode, the capacity ratio between the negative electrode and the positive electrode may be selected to be less than 1. In some cases, such as in NMF / NTP full cells, this can be achieved by making the mass ratio of the negative electrode material of the negative electrode to the positive electrode material of the positive electrode in the range of about 0.56:1 to about 0.95:1, for example, about 0.62:1 and about 0.75:1. When the mass ratio is reduced to about 0.62:1, the electrochemical device disclosed herein may experience almost no capacity decay after 160 cycles at 1C at 25°C. This strategy is to increase the mass of the positive electrode so that it exceeds the mass of the negative electrode to change the voltage of the electrochemical device to a voltage that only produces H2 and avoids the generation of O2. In addition, increasing the alkalinity of the electrolyte may also help to suppress the generation of H2. Then, the electrochemical device may achieve ideal stability.

[0057] The positive electrode and the negative electrode can be prepared by any method known in the art. For example, the electrode can be prepared by pressing a mixture of active material, support material (such as carbon black) and binder (such as polytetrafluoroethylene) on a stainless steel grid or titanium (Ti) mesh. Alternatively, the electrode can be made by applying a coating slurry on a metal foil (such as titanium (Ti), copper (Cu) and aluminum (Al)) or carbon paper, wherein the coating slurry contains an organic solvent, active material, conductive particles and binder.

[0058] For the electrochemical device disclosed herein, at least one layer of nanoparticles is disposed on the positive electrode. The at least one layer of nanoparticles can form a local hydronium-rich environment at the positive electrode during operation of the device, thereby suppressing the generation of oxygen at the positive electrode. Without being bound by any theory, it is believed that nanoparticles such as nickel-based nanoparticles can promote water dissociation, thereby generating a large amount of H in the at least one layer of nanoparticles due to water dissociation. + and OH - Then, Ni and OH - The strong interaction between - confined to the surface of the nanoparticle layer instead of escaping into the surrounding electrolyte. However, H + The interactions with Ni nanoparticles are poor and they tend to combine with nearby water molecules to form H3O around the nanoparticle layer. + , resulting in local H3O enrichment + environment.

[0059] The nanoparticles used herein may be based on Ni, Pt, Fe, Co, Pd and / or Cu, and may further comprise a carrier. Examples of carriers within the nanoparticles include, but are not limited to, carbon black, carbon nanotubes, graphite, graphitized carbon black, graphene, reduced graphene oxide (rGO), and combinations thereof. In order to form a layer of these nanoparticles, a membrane material such as Nafion-Na may be used. Nafion TM Perfluorosulfonic acid (PFSA) membranes are based on PFSA / polytetrafluoroethylene (PTFE) copolymers and have low ion transport resistance. Nafion TM The product is available from Chemours (formerly DuPont) in Delaware, USA as Nafion TM 117. Nafion TM 115. Nafion TM 212. Nafion TM 211 and other commercial acquisitions.

[0060] In some embodiments, the nanoparticles used herein may include Ni / C, Pt / C, Fe / C, Co / C, Pd / C, Cu / C, PtNi / C, PtFe / C, PtCo / C, PtCu / C, PdNi / C, Ni / rGO, Pt / rGO, Fe / rGO, Co / rGO, Cu / rGO, Pd / rGO, PtNi / rGO and PdNi / rGO nanoparticles. In some specific embodiments, the nanoparticles are selected from Ni / C, Fe / C, Co / C and Cu / C nanoparticles. Taking Ni / C nanoparticles as an example, they can be nanoparticles with a Ni loading of about 1wt% to 40wt%, such as about 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt% or 40wt%. It is preferred that the nanoparticles are Ni / C nanoparticles and / or Co / C nanoparticles, and the Ni loading and / or Co loading is from about 1wt% to about 40wt%, such as about 20wt%. Many of the nanoparticles mentioned herein are commercially available from Fuel CellStore, Texas, USA. Non-limiting examples include Vulcan with 10% nickel, Vulcan with 20% nickel, Vulcan with 40% nickel, Vulcan with 10% iron, Vulcan with 10% cobalt, and Vulcan with 40% platinum nickel (1:1 ratio).

[0061] The average particle size of the nanoparticles may be in the range of about 1 nm to about 100 nm. In some embodiments, the average particle size of the nanoparticles is in the range of 40 nm to 60 nm. The average particle size can be measured, for example, by transmission electron microscopy (TEM). See Figure 1 (b).

[0062] At least one layer of nanoparticles may have a thickness of about 5 μm to about 100 μm. If it is too thick, the cost will increase and the ion transport capability will be impaired. If it is too thin, at least one layer of nanoparticles may not be sufficient to form a local hydronium-rich environment at the positive electrode. The thickness can be measured by using a spectrometer.

[0063] The nanoparticles can be disposed on the positive electrode by solution casting. For example, the nanoparticles, the membrane material and the solvent are combined to prepare a solution, and then the solution is cast on the positive electrode. After the solvent is removed, the positive electrode will be coated with a nanoparticle layer.

[0064] The negative electrode and the positive electrode are connected to each other by an aqueous electrolyte. The aqueous electrolyte of the electrochemical device disclosed herein needs to have an alkaline pH. It is believed that increasing the pH helps to effectively suppress the generation of hydrogen at the anode. For the purposes of the present disclosure, the pH of the aqueous electrolyte may be selected to be in the range of about 9 to about 13, for example, about 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 and 13. In some embodiments, the pH of the aqueous electrolyte is about 12 to about 13. The aqueous electrolyte can be adjusted to the desired pH by using a suitable alkaline substance (such as NaOH and KOH).

[0065] The electrolyte plays a key role in transporting positive ions between the positive electrode and the negative electrode. When selecting an electrolyte for an aqueous electrolyte, at least the following factors may be considered: (i) chemical inertness; (ii) wide liquidus range and thermal stability; (iii) wide electrochemical stability window; (iv) high ionic conductivity and no electronic conductivity; (v) interfacial properties; and (vi) availability. In some cases, it may be desirable to modify the electrolyte disclosed herein by introducing a corrosion inhibitor or a complexing agent to reduce its corrosiveness. It is also possible to introduce additives into the aqueous electrolyte to optimize the electrochemical performance of the electrochemical device disclosed herein. For illustrative purposes, the electrolyte for ALIB may include LiPF6, LiClO4, LiAsF6, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), LiCF3SO3, and combinations thereof. The electrolyte for ASIB may include sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium nitrate (NaNO3), sodium sulfate (NaSO4), sodium chloride (NaCl), sodium acetate (CH3COONa), sodium carbonate (Na2CO3), sodium hexafluorophosphate (NaPF6), and combinations thereof. NaClO4 may be a preferred electrolyte salt for a low-cost, high-voltage sodium aqueous electrolyte having a wide electrochemical stability window.

[0066] In the case where the aqueous electrochemical device is an aqueous sodium ion battery, the aqueous electrolyte with an alkaline pH can be a water-in-salt electrolyte solution. It is believed that the formation of a solid electrolyte interface layer with a high salt concentration on the electrode surface can prevent water reduction, thereby having a positive effect on the wide electrochemical stability window. Preferably, the salt is selected from sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium nitrate (NaNO3), sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium acetate (CH3COONa), sodium carbonate (Na2CO3), sodium hexafluorophosphate (NaPF6) and combinations thereof. More preferably, the water-in-salt electrolyte solution is a saturated aqueous solution of sodium perchlorate. That is, at 25°C, the concentration of sodium perchlorate in the water-in-salt electrolyte is about 17 mol / kg, which is the highest value among other common sodium salts (such as CH3COONa: 5.7 mol / kg; NaCl: 6.1 mol / kg; NaNO3: 10.3 mol / kg).

[0067] When manufacturing the electrochemical device disclosed herein, other components such as diaphragms, adhesives, conductive agents and current collectors may also be used. The diaphragm provides a barrier without electrical conductivity between the negative electrode (anode) and the positive electrode (cathode), while allowing ions to be transferred from one electrode to the other. The diaphragm is expected to maintain chemical stability in the electrolyte while having a high affinity for the electrolyte. Non-limiting examples of diaphragms include glass fiber diaphragms, polyolefin diaphragms and non-woven diaphragms. When powdered materials are used for electrodes, adhesives may be added to the electrodes to bind the various components together and provide a uniform mix of the electrode components so as to allow the electrodes to conduct the required amount of electrons and ensure electronic contact during the cycling of the electrochemical device. Non-limiting examples of adhesives include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and carboxymethyl cellulose (CMC). Conductive agents can be used to enhance the conductivity of the electrode, and examples include but are not limited to carbon black, Ketjen black, graphene, conductive nanocarbon fibers (VGCF), carbon nanotubes (CNT) and multi-walled carbon nanotubes (MWCNT). The current collector is a bridging component that collects the current generated at the electrode and connects it to an external circuit. It may have a significant impact on the capacity, rate performance and long-term stability of the electrochemical device.Non-limiting examples of current collectors include aluminum foil, copper (Cu) foil, titanium (Ti) mesh, stainless steel mesh, carbon-coated aluminum, carbonaceous materials, and the like.

[0068] The aqueous electrochemical device disclosed herein can show advantages in many aspects, especially achieving significant improvements in electrochemical performance and stability. Therefore, the aqueous electrochemical device disclosed herein is very promising to meet the stringent requirements for electrochemical performance, stability, cost-effectiveness and safety.

[0069] In particular, the aqueous electrochemical device disclosed herein can exhibit about 82 Wh kg at 0.5C. -1 , or even at least about 90 Wh kg at 0.5C -1 Energy density. Energy density is a measure of the ratio of the energy contained in an electrochemical device to its weight. Energy density can be calculated using the following formula: Average battery discharge voltage (V) × battery discharge specific capacity (mAh) / total electrode weight (g) = specific energy or energy density (Wh / kg).

[0070] In addition, or as an alternative, the aqueous electrochemical device can have a cycle life of more than 14,000 cycles at 10C (1C = 118mA / g). In some cases, the aqueous electrochemical device can have a cycle life of up to 200 cycles at 1C, such as 200 cycles at 1C, 150 cycles at 1C, and 100 cycles at 1C. Cycle life is the number of charge and discharge cycles that an electrochemical device can complete before losing performance. The voltage range is 0.5 to 2.2V, and the temperature is 25°C. The battery is first charged to 2.2V at 25°C and then discharged to 0.5V.

[0071] Additionally or alternatively, the aqueous electrochemical device can exhibit 86% capacity retention at 0.5C (voltage range: 0.5V to 2.2V) after 200 cycles at -30°C. In addition, the aqueous electrochemical device can exhibit a high capacity of 32mAh and excellent stability under harsh conditions.

[0072] In the case of about 20 mg cm -2 In the case of Na2MnFe(CN)6 / NaTi2(PO4)3 soft-pack cells with similar electrode loading, the aqueous electrochemical device exhibits an average Coulombic efficiency of 99% at 1C and retains 85% of its capacity after 1000 cycles. -2 In the case of a 50mAh Na2MnFe(CN)6 / NaTi2(PO4)3 soft pack battery, the aqueous electrochemical device can deliver 300mAg at 25°C. -1 After 200 cycles, the capacity retention rate is close to 100%.

[0073] On this basis, a method for manufacturing an aqueous electrochemical device is developed herein, the device comprising a negative electrode, a positive electrode, a separator and an aqueous electrolyte having an alkaline pH. The method includes applying at least one layer of nanoparticles capable of forming a local hydronium-rich environment at the positive electrode during operation of the device on the positive electrode, and / or making the capacity ratio between the negative electrode and the positive electrode less than 1 (i.e., N / P capacity ratio <1) to substantially avoid the generation of oxygen at the positive electrode. Methods for manufacturing electrochemical devices (such as batteries) are known in the art and can be adapted to the present disclosure. At least one layer of nanoparticles for forming a local hydronium-rich environment at the positive electrode can be appropriately selected and applied to the positive electrode with reference to the detailed description and examples herein.

[0074] Also disclosed herein is a positive electrode for an aqueous electrochemical device, on which is disposed at least one layer of nanoparticles capable of forming a local hydronium-rich environment at the positive electrode during device operation. The nanoparticles, at least one layer of nanoparticles, the positive electrode, and the electrochemical device may be those described herein above.

[0075] Also disclosed herein is a method for preparing a positive electrode for an aqueous electrochemical device, wherein the method includes applying at least one layer of nanoparticles capable of forming a local hydronium-rich environment at the positive electrode during device operation on the positive electrode. The nanoparticles, at least one layer of nanoparticles, the positive electrode, and the electrochemical device may be those described herein above.

[0076] Surface treatment of the positive electrode by at least one layer of nanoparticles can induce a local hydronium-rich environment at the positive electrode in an aqueous electrolyte with an alkaline pH. The inventors have found that this surface treatment can be used to suppress oxygen generation at the positive electrode and stabilize the positive electrode. In the case of a manganese-rich Prussian blue analog (PBA) such as Na2MnFe(CN)6 as the positive electrode material and at least one layer of nickel-based nanoparticles on the positive electrode, the inventors have found that the formation of a local hydronium-rich environment at the positive electrode in an alkaline (or high pH) electrolyte can also promote Ni 2+ In-situ replacement of Mn, thereby enhancing the stability of the aqueous electrochemical device. On this basis, significant improvements in the electrochemical performance and stability of the aqueous electrochemical device can be achieved. In addition, or as an alternative, the capacity ratio of the negative electrode to the positive electrode can be selected to be less than 1 to substantially avoid the generation of oxygen at the positive electrode. This cathode sacrificial strategy, combined with an alkaline pH (or high pH) electrolyte that helps to suppress the generation of hydrogen at the negative electrode, can also help improve the electrochemical performance and stability of the aqueous electrochemical device. It is expected that the aqueous electrochemical device disclosed herein may find particular use in large-scale energy storage.

[0077] Example

[0078] Experiments involving application of at least one layer of nanoparticles

[0079] Preparation of materials

[0080] Na2MnFe(CN)6 was synthesized by coprecipitation 17 . 5mmol Na4Fe(CN)6 (Sigma-aldrich) and 15gNaCl (Sigma-aldrich) were dissolved in 100mL deionized water to form solution A. 5mmol MnCl2 (Sigma-aldrich) was dissolved in 50mL deionized water to form solution B. Then, solution B was slowly (about 20 minutes) added dropwise to solution A under stirring, and then stirring was continued for 2 hours. The solid phase was obtained by centrifuging the prepared solution and washing it three times with 30mL deionized water. Then, the solid phase was dried and ground into powder and used after drying in a vacuum oven at 110°C for 24 hours.

[0081] NaTi2(PO4)3 / C was synthesized by sol-gel method. 17 . Typically, 2.5 mmol CH3COONa·3H2O (Sigma-aldrich) and 7.5 mmol NH4H2PO4 (Sigma-aldrich) were dissolved in 100 mL of deionized water to form solution C. 0.4 g of polyvinyl pyrrolidone (Sigma-aldrich) and 5 mmol Ti(CH3CH2CH2CH2O)4(TCI) (Sigma-aldrich) were dissolved in 50 mL of anhydrous ethanol to form solution D. Next, solution D was quickly poured into solution C and stirred vigorously, and then the resulting mixed solution was continuously stirred for 3 hours, and the solvent was evaporated and removed at 80°C to prepare a precursor. The resulting precursor was ground and calcined at 800°C for 12 hours in an argon gas flow to obtain an NTP / C complex. The carbon content of the NTP / C complex was 5%.

[0082] Nafion-Na was prepared by the following method: purchased Nafion TM 115 (DuPont, D520, 5 wt%) was neutralized dropwise with 0.01 M NaOH solution to pH = 7. Subsequently, the solution was ion exchanged in distilled water for 12 hours. Finally, the product was collected after removing the solvent at 60°C.

[0083] Preparation of Na2MnFe(CN)6(NMF) positive electrode and NaTi2(PO4)3(NTP) negative electrode

[0084] The NMF positive electrode was prepared by mechanically mixing 80 wt% NMF, 10 wt% SuperP carbon black, and 10 wt% polytetrafluoroethylene (PTFE) binder (dispersed in ethanol solvent). The mixture was then pressed onto a Ti mesh at a pressure of 6 MPa and dried at 70 °C for 2 hours. The NTP negative electrode was prepared by the same procedure using 80 wt% NTP, 10 wt% SuperP carbon black, and 10 wt% PTFE. The mass loading of the electrode was about 20 mg / cm 2 . N / P is about 1.05 to 1.

[0085] Preparation of aqueous electrolyte

[0086] 41.6 g NaClO4 was dissolved in 20 mL water to obtain 17 M NaClO4. Alkaline electrolyte was obtained by adding required amount (0.1 mL, 0.2 mL, 0.4 mL) of 1 mol / L NaOH aqueous solution to 30 mL 17 M NaClO4. The pH of the electrolyte was 12.75. In order to eliminate the influence of concentration variation, pure water of the same amount (0.1 mL, 0.2 mL, 0.4 mL) was added to 17 M NaClO4 to obtain a neutral electrolyte.

[0087] Applying a nanoparticle layer on the positive electrode

[0088] The nanoparticle solution was prepared as follows: 0.1 g of Nafion-Na was dissolved in a mixed solution of 0.45 g of N,N-dimethylformamide (DMF) and 0.9 g of isopropanol at 60°C; then 0.025 g of Ni / C (Ni loading of 20%, purchased from Fuel Cell Store, Texas, USA) was added to the above solution, stirred for 0.5 hour and ultrasonicated for 0.5 hour. The above steps were repeated three times to obtain a uniform mixture. Then, 10 μL of the solution was added dropwise to the surface of the positive electrode disc. After removing the solvent at room temperature, the positive electrode disc was coated with a nickel-based nanoparticle layer. The particle size of the nickel-based nanoparticles was about 50 nm, and the thickness of the nanoparticle layer was about 5 μm.

[0089] Button battery assembly

[0090] Place the negative electrode on the smaller cell cover. Place the glass fiber separator as centered as possible on the negative electrode and drip the required amount of electrolyte on the separator. Place the positive electrode on top of the separator with the cast nanoparticle layer facing the negative electrode. Center the positive and negative electrodes as much as possible to avoid uneven current density. Place the stainless steel mesh and spring in order. Place the larger cover on top and press to seal.

[0091] Assembly of soft pack batteries

[0092] The pouch cell is assembled using a stacking machine, with a glass fiber separator placed between the electrodes to form a stack inserted into the pouch. The sides of the pouch are joined together by heat sealing, leaving one side open. Liquid electrolyte is then added to the cell using an electrolyte filling system. The cell is then sealed using a vacuum sealer to complete the pouch cell assembly.

[0093] result

[0094] As shown in Figure 1 and Figure 2 As shown, at the cathode, the onset of OER has been postponed from 1 V to 1.2 V by applying a 20% Ni / C nanoparticle layer to create a local hydronium-rich environment.

[0095] In sodium aqueous batteries, applying a Ni / C nanoparticle layer to create a local hydronium-rich environment at the cathode unexpectedly improves the electrochemical performance of NMF / NTP cells. Figure 3 As shown, NMF / NTP full cells cycled in neutral and alkaline electrolytes show very poor rate performance, as well as low Coulombic efficiency at low rates (less than 80% in neutral electrolyte and less than 85% in alkaline electrolyte at 0.5C) and low capacity at high rates (less than 40 mAh g -1 In sharp contrast, after applying the Ni / C nanoparticle layer on the cathode, the battery exhibited 118, 117, 100, and 88 mAh g at current densities of 0.5C, 1C, 5C, and 10C, respectively. -1 The reversible capacity ( Figure 4 a). The cells applying Ni / C nanoparticle layer on the positive electrode showed impressive stability at high rates. In addition, the gradually decreasing discharge average voltage (DAV) of the cells cycled in neutral and alkaline electrolytes also indicated the instability of aqueous batteries, which would compromise the energy density during cycling and storage ( Figure 4 b). However, the surface treatment of the positive electrode can effectively stabilize the DAV at low rates and ensure that the battery has a high DAV (about 1.2V) at a high rate of 10C. Then, the cycling performance of the battery was examined at a low rate of 0.5C ( Figure 5 ). The capacity of the battery using the cathode surface treatment is much higher than that of other systems. More importantly, the battery cycled in a neutral electrolyte showed a very low Coulombic efficiency, which was less than 80% and gradually decreased due to severe side reactions. After adding NaOH to the electrolyte to increase the pH, the Coulombic efficiency increased to 85% due to the suppression of HER. However, after applying a Ni / C nanoparticle layer on the cathode, the Coulombic efficiency increased significantly to more than 96%. The battery with the cathode surface treatment can also achieve improved performance at 1C without obvious capacity decay ( Figure 4c). More importantly, the battery with positive electrode surface treatment can be stably cycled in a harsh environment of -30°C, and the capacity retention rate is 86% after 200 cycles at 0.5C ( Figure 4 d), which exceeds most previously reported aqueous batteries 18-19 Most importantly, the cells with cathode surface treatment achieved an unprecedented long cycle life of more than 14,000 cycles at 10C and high performance at high electrode loadings (about 20 mg cm -1 , Figure 4 e) has a favorable capacity retention of 56%.

[0096] The present work is compared with previously reported work. Figure 6 As shown in Table 1, among the recently reported sodium aqueous batteries, the battery according to the present disclosure has the highest electrode loading and energy density, the longest life and the lowest cost. Even though the average voltage is limited due to the limitation of the electrode, it can still reach a high value of 1.4V. Compared with the recently reported aqueous lithium, sodium, and potassium batteries with good stability using expensive fluoride-containing salts, our work uses cheap NaClO4 monoaqueous solution, which produces an undeniable advantage. As shown in Figure 7a (the price of the salt is based on the data of Australian Sigma and the cost of the solvent is ignored), the cost of conventional WIS electrolytes is very high, such as 21M bis(trifluoromethane)sulfonyl imide lithium salt (LiTFSI) 2 , 21M KOTF 19 and 9M NaOTF 20 Some researchers have introduced large amounts of organic solvents to reduce salt usage and costs, but this has raised safety concerns. 21-23. In sharp contrast, by using a monoaqueous NaClO4 solution and a surface treatment strategy, the electrochemical device of the present disclosure can achieve good electrochemical performance at a very low cost (at most 1 / 40 of the conventional WIS strategy based on fluoride salts). Due to the relatively limited reserves and high prices of lithium, aqueous lithium-ion batteries may not be suitable for large-scale energy storage. Therefore, the inventors compared recently reported aqueous sodium and potassium batteries in terms of energy density and life (Figure 7b). Even though the energy density of the ASIB according to the present disclosure is slightly lower than that of a previously reported work due to limitations of the electrodes. However, the life of the battery according to the present disclosure (14,000 cycles) is twice that of the second place (6,500 cycles). The ASIB according to the present disclosure is a promising candidate for practical application in large-scale energy storage. The inventors then compared the ASIB with other electrochemical energy storage systems. As shown in FIG. 7c and Table 2, even though the energy density of the ASIB according to the present disclosure is lower than that of lithium-ion batteries and nickel-manganese batteries, it exhibits significant advantages over all other batteries in terms of key element abundance, safety, environmental friendliness, and has an ultra-long life, which makes it a promising candidate for large-scale energy storage.

[0097] Table 1 Comparison of recently reported sodium aqueous batteries

[0098]

[0099] Table 2 Comparison of our work with commercial batteries

[0100]

[0101] Safety is one of the key parameters for evaluating the effectiveness of battery systems suitable for large-scale energy storage. Therefore, the inventors assembled NMF / NTP batteries to test them under very harsh environments. Figure 8 As shown in a, the output voltage of the soft-pack battery is 1.775V, which is much higher than that of conventional sodium aqueous batteries. Thanks to this high voltage, two batteries can power a blue light lamp (the minimum voltage requirement of a blue light lamp is 3V). More interestingly, the soft-pack battery showed unparalleled stability in the cutting experiment ( Figure 8 c). The soft pack battery can be cut and immersed in water without affecting its function of powering the light. The high capacity of the soft pack battery also shows strong performance in powering the electric fan before or after being cut and immersed in water ( Figure 8 e). In addition, the soft pack battery can be recharged to 2.2V after being cut and used to power the fan in water, which shows excellent stability ( Figure 8 f). Most importantly, the recharged cut pouch cell can continuously power the hygrometer in water for more than 10 hours ( Figure 8This means that the battery can withstand electrolyte leakage in high humidity environments (even in water) without causing serious damage to the entire system while maintaining the ability to power electrical devices, leading to greatly improved safety of large-scale energy storage and a variety of applications in underwater electrical devices.

[0102] discuss

[0103] The unprecedented electrochemical performance of the electrochemical device of the present disclosure can be attributed to the local hydronium-rich environment created at the positive electrode. To test this hypothesis, in situ IR spectroscopy was used to verify the presence of H3O + The generation of Fig. 9 a and 9b). In order to exclude the influence of electrolyte and nanoparticles themselves, the reference spectrum (no potential applied) was used as the background for each set of tests. Carbon black (C) was used as a control group to eliminate the influence of polymer support and carbon black itself. As expected, the spectrum of C did not change significantly even when the voltage was increased to 1.3 V, indicating that C and the polymer support could not create a local hydronium-rich environment. In contrast, for Ni / C in an alkaline electrolyte, a new peak appeared when the applied potential was higher than 0.6 V. At 2218 cm -1 and 1810cm -1 The peak at can be attributed to H3O + The two asymmetric OH stretching modes ( and Fig. 9 a). In addition, the spectrum also shows a -1 H3O + The resonance peak of the asymmetric OH stretching mode and at 1230cm -1 The corresponding + Umbrella vibration The obvious and isolated peak ( Fig. 9 b) In summary, in situ IR is H3O + The generation of provides clear evidence.

[0104] Ni / C coating( Fig. 9 d) A gap is created between the coating and the cathode layer, which can accommodate H3O + Ni nanoparticles can promote the dissociation of water, which has been demonstrated in previous catalytic studies. 25,26 Therefore, due to water dissociation, a large amount of H + and OH - ,like Fig.9e As shown. Ni and OH - The strong interaction between -confined on the surface of Ni nanoparticles, making it difficult for them to escape into the surrounding solution. + The interaction with Ni nanoparticles is poor in alkaline media and will combine with nearby water molecules to form H3O + These H3O exposed to the bulk alkaline electrolyte + ions will be easily replaced by excess OH - On the contrary, due to the barrier effect of the coating, H3O + ions will accumulate under the layer, forming H3O-rich + environment, thereby suppressing OER during battery operation.

[0105] The high pH of the electrolyte not only leads to aqueous OER but also exacerbates the problem of cathode dissolution. Prussian blue analogs (PBAs) are promising cathode materials for sodium batteries because they are environmentally friendly and have a facile intercalation / deintercalation mechanism. 27,28 However, hydroxide anions can interact with N-coordinated metal atoms and then destroy the PBA 29,30 In addition, some OH - Species will also adsorb on the cathode close to the OER operating potential, further promoting harmful side reactions 31 In addition, this problem is more serious in manganese-rich PBA such as NMF due to the 3+ The disproportionation reaction and Jahn-Teller (JT) distortion drive the Mn dissolution. 32 .like Fig.11 As shown in Figs. a and 11b, the second plateau is missing in the charge-discharge curves of the NMF / NTP electrode in neutral and alkaline electrolytes for the reasons mentioned above. However, for the battery with surface treatment applied on the positive electrode, the second plateau is very stable even after 40 cycles ( Fig.11 c) It is believed that there are two main contributions to the ultrahigh stability of PBA cathodes in alkaline electrolytes. First, as mentioned above, a local hydronium-rich environment at the cathode is created by the cathode surface treatment. Then, the H3O-rich + The surface layer prevents OH - Species adsorb on the cathode surface, thus reducing the dissolution of Mn. 33 If electrochemically active cations (such as Ni 2+ and Co 2+ ) to replace Mn, which can improve the capacity and cycling performance of Mn-based electrodes. Therefore, it is believed that this abnormal stability of NMF can also be attributed to the oxidation of Ni particles in the nanoparticle layer during charging. 2+ In this regard, Raman spectroscopy was applied to verify this hypothesis ( Fig.11 d). 2050 to 2200 cm in Raman spectrum-1 Peaks in the range are assigned to CN - Group, indicating that - The transition metal ions bound to the groups exhibit different valence states 34 In the Raman spectra of NMF electrodes cycled in neutral and alkaline electrolytes, the -1 and 2158cm -1 There are three peaks at 2+ -N≡C-Mn 2+ and Fe 2+ -N≡C-Mn 3+ In contrast, the Raman spectrum of the surface-treated cathode cycled in an alkaline electrolyte shows a peak at 2130 cm -1 and 2150cm -1 In addition, at 2163cm -1 The Fe 2+ -N≡C-Ni 2+ All these changes indicate that Ni is introduced into the structure of NMF after cycling in an alkaline electrolyte with a local microenvironment (LME). Then, TEM and EDS spectroscopy were also used to verify the presence of Ni in the cathode. Fig.11 As shown in Figure 5, after applying the nanoparticle layer, the crystal structure of NMF is well maintained, but the crystal structure is destroyed in neutral and alkaline electrolytes. The EDS of the cycled NMF cathode also indicates the presence of a Ni peak at 0.82 keV ( Fig.11 f).

[0106] In summary, it has been demonstrated that the surface treatment strategy disclosed in this article can greatly improve the stability of aqueous electrolytes as well as the stability of Mn-based cathodes without compromising the low cost and environmental friendliness of sodium aqueous batteries. This strategy can achieve ultra-long life and high energy density sodium aqueous batteries while maintaining cost-effectiveness, environmental friendliness and low temperature tolerance. More importantly, the pouch cells using the positive electrode surface treatment strategy can achieve unprecedented stability even after being cut and immersed in water. This represents a major advance in aqueous battery design, both conceptually and in actual demonstration, and sets new performance standards, which is expected to produce battery systems that exceed previous energy density and practical application limits, while reducing or eliminating the need to change the battery industry infrastructure, with high compatibility with current commercial lithium-ion battery and sodium-ion battery systems, and without the need for expensive anhydrous processes and safety management required for flammable electrolytes. It is believed that batteries based on this strategy can promote the application of aqueous batteries in large-scale energy storage and underwater devices because they use abundant raw materials, low cost, environmental friendliness, long life, ultra-high stability, safety in aqueous environments, and favorable energy density.

[0107] In addition to Ni, other metal nanoparticles including Pd, Cu, and Co ( Fig.12 ). Co nanoparticles can also effectively stabilize NMF / NTP batteries in alkaline electrolytes. This demonstrates the applicability of creating a local environment to put high-performance alkaline ASIBs into practice.

[0108] Experiments related to the cathode sacrificial strategy

[0109] Preparation of Na2MnFe(CN)6(NMF) positive electrode and NaTi2(PO4)3(NTP) negative electrode

[0110] NMF and NTP were prepared as described above, except that no nanoparticle layer was applied on the cathode surface.

[0111] Preparation of aqueous electrolyte

[0112] The aqueous electrolyte was prepared as described above.

[0113] Results and Discussion

[0114] In some cases, the mass ratio between the negative electrode and the positive electrode can be reduced to less than 1 to improve the stability of the battery. When the mass ratio of NTP / NMF is 1:1, the battery exhibits rapid capacity decay at 1C at 25°C in the absence of a nanoparticle layer. However, if the mass ratio between NTP and NMF is reduced to 0.75:1, the stability of the battery can be greatly improved, and the battery capacity retention rate at 25°C at 1C reaches 90% ( Fig.13 When the mass ratio between NTP and NMF is reduced to 0.62:1, the stability of the battery is further improved ( Fig.14 When the mass ratio is reduced to 0.56:1, the battery retains 90% of its capacity at a high rate of 10C (compared to the capacity at 1C, Fig.15 After 1600 cycles at 25°C, it also maintained a capacity retention rate of nearly 100% at 10°C ( Fig.15 ).

[0115] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.

[0116] It should be understood that, unless otherwise stated or implied, the terms "comprise" and "include" and any derivatives thereof (e.g., comprises, comprising, includes, including) used in this specification and the following claims should be construed as including the features referred to by the terms and not meant to exclude the presence of any additional features.

[0117] In some cases, for the sake of brevity and / or to help understand the scope of the present disclosure, a single embodiment may combine multiple features. It should be understood that in this case, these multiple features may be provided separately (in separate embodiments) or in any other suitable combination. Alternatively, when separate features are described in separate embodiments, unless otherwise specified or implied, these separate features may be combined into a single embodiment. This also applies to the claims, which may be recombined in any combination. That is, the claims may be amended to include features defined in any other claim. In addition, a phrase referring to "at least one" in a list of items refers to any combination of these items, including single members. For example, "at least one of a, b, or c" is intended to cover: a, b, c, ab, ac, bc, and abc.

[0118] Those skilled in the art will appreciate that the present disclosure is not limited to the specific applications described. The present disclosure is also not limited to the preferred embodiments of the specific elements and / or features described or depicted herein. It should be understood that the present disclosure is not limited to the disclosed one or more embodiments, but is capable of a variety of rearrangements, modifications and substitutions without departing from the scope set forth and defined by the following claims.

[0119] References

[0120] [1]Niu,C.et al.Balancing interfacial reactions to achieve longcycling life in high-energy lithium metal batteries.Nature Energy 6,723-732(2021).

[0121] [2]Zheng,Q.et al.A cyclic phosphate-based battery electrolyte for high voltage and safe operation.Nature Energy 5,291-298(2020).

[0122] [3]Hu,L.et al.Nonflammable electrolyte enhances batterysafety.Proceedings of the National Academy of Sciences 111,3205-3206(2014).

[0123] [4]Hammami,A.et al.Runaway risk of forming toxic compounds.Nature424,635-636(2003).

[0124] [5]Xu,C.et al.Nature-inspired hierarchical materials for sensing andenergy storage applications.Chemical Society Reviews 50,4856-4871(2021).

[0125] [6]Chen,W.et al.A manganese–hydrogen battery with potential for grid-scale energy storage.Nature Energy 3,428-435(2018).

[0126] [7]Soloveichik,G.L.J.N.Metal-free energy storage.Nature 505,163-164(2014).

[0127] [8]Suo,L.et al.“Water-in-salt”electrolyte enables high-voltageaqueous lithium-ion chemistries.Science 350,938-943(2015).

[0128] [9]Abraham,K.J.A.E.L.How comparable are sodium-ion batteries tolithium-ion counterparts?ACS Energy Letters 5,3544-3547(2020).

[0129]

[10] Jiang,L.et al.Building aqueous K-ion batteries for energystorage.Nature Energy 4,495-503(2019).

[0130]

[11] Xue,L.et al.Cathode dependence of liquid-alloy Na–Kanodes.Journal of the American Chemical Society 140,3292-3298(2018).

[0131]

[12] Zhou,A.et al.Size-,water-,and defect-regulated potassiummanganese hexacyanoferrate with superior cycling stability and ratecapability for low-cost sodium-ion batteries.Small 15,1902420(2019).

[0132]

[13] Jiang,L.et al.High-voltage aqueous Na-ion battery enabled byinert-cation-assisted water-in-salt electrolyte.Advanced Materials 32,1904427(2020).

[0133]

[14] Li,W.et al.Lithium intercalation from aqueous solutions.Journalof the Electrochemical Society 141,2310(1994).

[0134]

[15] Luo,J.-Y.et al.Raising the cycling stability of aqueous lithium-ion batteries by eliminating oxygen in the electrolyte.Nature chemistry 2,760-765(2010).

[0135]

[16] Kim,H.et al.Aqueous rechargeable Li and Na ion batteries.ChemicalReviews 114,11788-11827(2014).

[0136]

[17] Han,J.et al.Fluorine-free water-in-salt electrolyte for green andlow-cost aqueous sodium-ion batteries.ChemSusChem 11,3704-3707(2018).

[0137]

[18] Jiang,L.et al.Building aqueous K-ion batteries for energystorage.Nature Energy 4,495-503(2019).

[0138]

[19] Ge,J.et al.Surface-substituted Prussian blue analogue cathode forsustainable potassium-ion batteries.Nature Sustainability,1-10(2021).

[0139]

[20] Suo,L.et al.“Water-in-salt”electrolyte makes aqueous sodium-ionbattery safe,green,and long-lasting.Advanced Energy Materials 7,1701189(2017).

[0140]

[21] Xu,J.et al.Aqueous electrolyte design for super-stable 2.5 VLiMn2O4||Li4Ti5O 12 pouch cells.Nature Energy 7,186-193(2022).

[0141]

[22] Xie,J.et al.Molecular crowding electrolytes for high-voltageaqueous batteries.Nature materials 19,1006-1011(2020).

[0142]

[23] Shang,Y.et al.An“ether-in-water”electrolyte boosts stableinterfacial chemistry for aqueous lithium-ion batteries.Advanced Materials32,2004017(2020).

[0143]

[24] Wang,X.et al.Anomalous hydrogen evolution behavior in high-pHenvironment induced by locally generated hydronium ions.Nature communications10,1-8(2019).

[0144]

[25] Ghosh,S.et al.Multifold enhancement in water dissociation withAg / Ni bimetallic alloy surfaces.Surface Science 701,121695(2020).

[0145]

[26] Hundt,P.M.et al.Vibrationally promoted dissociation of water onNi(111).Science 344,504-507(2014).

[0146]

[27] Zhu,K.et al.Low defects potassium cobalt hexacyanoferrate as asuperior cathode for aqueous potassium ion batteries.Journal of MaterialsChemistry A 8,21103-21109(2020).

[0147]

[28] Li,L.et al.A Low-Strain Potassium-Rich Prussian Blue AnalogueCathode for High Power Potassium-Ion Batteries.Angewandte ChemieInternational Edition 60,13050-13056(2021).

[0148]

[29] Yang,Y.et al.Quantitative measurement of cyanide released fromPrussian Blue.Clinical Toxicology 45,776-781(2007).

[0149]

[30] Stilwell,D.et al.Electrochemical studies of the factorsinfluencing the cycle stability of Prussian Blue films.Journal of AppliedElectrochemistry 22,325-331(1992).

[0150]

[31] Lamprecht,X.et al.Electrolyte effects on the stabilization ofprussian blue analogue electrodes in aqueous sodium-ion batteries.ACS AppliedMaterials 2022,14,2,3515–3525(2022).

[0151]

[32] Thackeray,M.et al.Electrochemical extraction of lithium fromLiMn2O4.Materials Research Bulletin 19,179-187(1984).

[0152]

[33] Zhan,C.et al.Dissolution,migration,and deposition of transitionmetal ions in Li-ion batteries exemplified by Mn-based cathodes–a criticalreview.Energy Environmental Science 11,243-257(2018).

[0153]

[34] Li,W.et al.Stress distortion restraint to boost the sodium ionstorage performance of a novel binary hexacyanoferrate.Advanced EnergyMaterials 10,1903006(2020).

Claims

1. An aqueous electrochemical device comprising a negative electrode, a positive electrode, a separator and an aqueous electrolyte having an alkaline pH, wherein the positive electrode is provided with at least one layer of nanoparticles capable of forming a local hydronium ion-rich environment at the positive electrode during operation of the device, and / or the capacity ratio between the negative electrode and the positive electrode is less than 1 to substantially avoid the generation of oxygen at the positive electrode.

2. A method for manufacturing an aqueous electrochemical device, the aqueous electrochemical device comprising a negative electrode, a positive electrode, a separator and an aqueous electrolyte having an alkaline pH, wherein the method comprises applying at least one layer of nanoparticles on the positive electrode that can be used to form a local hydronium ion-rich environment at the positive electrode during operation of the device, and / or making the capacity ratio between the negative electrode and the positive electrode less than 1 to substantially avoid the generation of oxygen at the positive electrode.

3. The device and method according to any one of claims 1 to 2, wherein the aqueous battery is an aqueous metal ion battery.

4. The device and method according to claim 3, wherein the aqueous battery is an aqueous lithium ion battery, an aqueous sodium ion battery or an aqueous potassium ion battery.

5. The device and method according to any one of claims 1 to 4, wherein the nanoparticles are made of a carrier and any one selected from Ni, Pt, Fe, Co, Pd, Cu and combinations thereof.

6. The device and method according to claim 5, wherein the carrier within the nanoparticles is selected from carbon black, carbon nanotubes, graphite, graphitized carbon black, graphene, reduced graphene oxide, and combinations thereof.

7. The device and method according to any one of claims 1 to 6, wherein the nanoparticles are selected from Ni / C, Pt / C, Fe / C, Co / C, Pd / C, Cu / C, PtNi / C, PtFe / C, PtCo / C, PtCu / C, PdNi / C, Ni / rGO, Pt / rGO, Fe / rGO, Co / rGO, Pd / rGO, Cu / rGO, PtNi / rGO and PdNi / rGO nanoparticles.

8. The apparatus and method of claim 7, wherein the nanoparticles are Ni / C and / or Co / C nanoparticles having a Ni and / or Co loading of about 1 wt% to about 40 wt%.

9. The device and method according to any one of claims 1 to 8, wherein the average particle size of the nanoparticles ranges from about 1 nm to about 100 nm.

10. The device and method according to any one of claims 1 to 9, wherein the thickness of the at least one layer of nanoparticles is about 5 μm to 100 μm.

11. The device and method of any one of claims 1 to 10, wherein the pH of the aqueous electrolyte is from about 9 to about 13.

12. The device and method according to any one of claims 1 to 11, wherein the aqueous electrochemical device is an aqueous sodium ion battery, and the aqueous electrolyte with an alkaline pH comprises a salt as an electrolyte, the salt being selected from sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaCF3SO3), sodium nitrate (NaNO3), sodium chloride (NaCl), sodium sulfate (Na2SO4), sodium acetate (CH3COONa), sodium carbonate (Na2CO3), sodium hexafluorophosphate (NaPF6) and combinations thereof.

13. The apparatus and method of claim 12, wherein the aqueous electrolyte having an alkaline pH is a saturated aqueous solution of sodium perchlorate.

14. The device and method according to any one of claims 1 to 13, wherein the aqueous electrochemical device is an aqueous sodium ion battery, and the positive electrode comprises a positive electrode material selected from the group consisting of: Na x Fe y Mn 1-y [Fe(CN)6] w ·zH2O(1≤x≤2,0.8≤y≤1,0.8≤w≤1,0.5≤z≤2), Na2Mn x Fe 1-x Fe(CN)6(0.8≤x≤1), Na2Mn x Ni 1-x Fe(CN)6(0.8≤x≤1), Na2Mn x Co 1-x Fe(CN)6(0.8≤x≤1.0), Na3V2(PO4)2F3, Na 0.44 MnO2, Na2NiFe(CN)6, Na2CuFe(CN)6, Na2NiMn(CN)6, Na3V2(PO)4, NaMnO2, Na 0.66 [Mn 0.66 Ti 0.34 ]O2, and Na2Zn3[Fe(CN)6]2, Na3MnTi(PO4)3 and Na4Fe3(PO4)2(P2O7).

15. The device and method according to any one of claims 1 to 14, wherein the aqueous electrochemical device is an aqueous sodium ion battery, and the negative electrode comprises a negative electrode material selected from the group consisting of NaTi2(PO4)3, Na3MnTi(PO4)3, NaTiOPO4, Na2VTi(PO4)3, Na3V2(PO4)3, TiSe2, TiS2, hard carbon and perylenetetracarboxylic acid diimide.

16. The device and method of any one of claims 1 to 15, wherein the capacity ratio between the negative electrode and the positive electrode is from about 0.56:1 to about 0.95:

1.

17. The device and method of claim 16, wherein the capacity ratio between the negative electrode and the positive electrode is about 0.62:

1.

18. The device and method of claim 16, wherein the capacity ratio between the negative electrode and the positive electrode is about 0.75:

1.

19. A cathode for an aqueous electrochemical device having disposed thereon at least one layer of nanoparticles capable of forming a localized hydronium ion-rich environment at the cathode during operation of the device.

20. A method of preparing a cathode for an aqueous electrochemical device, wherein the method comprises applying to the cathode at least one layer of nanoparticles capable of forming a localized hydronium ion-rich environment at the cathode during operation of the device.

Images