Electrolyte additive for Zn-MnO2 batteries

Abstract

An electrolyte composition for a Zn-MnO2 electrochemical device, the electrolyte comprising water, zinc sulfate, and urea; a use of the electrolyte composition; and an electrochemical device comprising the electrolyte.

Description

Technical Field

[0001] The present invention relates to Zn-MnO2 electrochemical devices, such as battery cells and batteries, and more specifically, to an electrolyte additive and composition particularly suitable for such devices. Background Technology

[0002] Zn-MnO2 batteries (i.e., electrochemical cell units and cells with zinc and manganese dioxide electrodes) have a power output of 80 to 190 Wh·kg⁻¹. -1 The energy density of zinc-ion batteries is commonly used in home electronics and medical units. Research on zinc-ion battery cells began in the early days of the development of electrochemical devices, as they were used as anodes in Volta's pile in 1800 and Daniel's pile in 1836. Leclanché demonstrated the first Zn-MnO2 battery cell based on a saltwater electrolyte, followed by an alkaline galvanic cell in 1950, with an energy density of 80 to 190 Wh·kg⁻¹. -1 With its high energy density, this battery is still used in home electronics and medical units. Although many studies have attempted to make Zn-MnO2 alkaline batteries rechargeable using KOH-based gels, this goal has never been achieved due to key issues such as zinc passivation and H2 gas evolution (primarily caused by the thermodynamic instability of zinc in alkaline pH). In 1986, Yamamoto et al. 1-3 This represents a significant step forward in rechargeable Zn-MnO2 batteries by using a ZnSO4-based aqueous electrolyte. The system addresses anode-side stability issues by employing a weakly acidic pH. However, this is not entirely satisfactory due to its limited cycle life of approximately 25 cycles and the presence of a significant dead weight mass on the cathode side, with a specific capacity approaching 100-200 mAh / g. 4 The proposal suggested reducing the areal loading and adding MnSO4 to the electrolyte to improve reversibility to 100 cycles. Although later studies achieved over 5000 cycles, the Zn-MnO2 coin cell consistently exhibited low electrode loading (<1 mg / cm²) at high rates (>5 C). 2 Cycling with these cells yielded a specific capacity of no more than 300 mAh / g. These individual cells failed to meet commercial requirements. Furthermore, improvements experienced several slowdowns due to the uncertain chemo-electrochemical reaction mechanism. Although at least four explanations have been proposed, the electrochemistry behind the system remains unclear. Regardless of the MnO2 conversion mechanism, it has been reported that the pH increase caused by proton consumption during the MnO2 conversion reaction leads to the precipitation of zinc layered double hydroxides. Given zinc's poor stability at extreme pH levels, this pH variation is considered a key issue for system sustainability.

[0003] Recently, ICP-MS quantitatively confirmed that the main electrochemical reaction is driven by the dissolution / precipitation of MnO2. A new explanation for the precipitation / dissolution process of ZHS (zinc hydroxide sulfate) has been proposed, which may involve the complex sol-gel chemistry of the metal cations. 4,5 This type of reaction causes a sudden pH change at the cathode interface, leading to the precipitation of ZnSO4 electrolyte as ZHS (zinc hydroxide sulfate). Contrary to the assumptions of the 1990s, this process may not be entirely undesirable, as it buffers the pH through its highly reversible chemical precipitation / dissolution. [7,8] However, due to rapid precipitation, it can also cause passivation of the cathode material. This has been demonstrated in alkaline batteries.

[0004] Therefore, rechargeable Zn-MnO2 battery cells still exhibit key issues in capacity retention, poor specific capacity (not exceeding 300 mAh / g, compared to a theoretical capacity of 617 mAh / g), and dendrite growth. Most importantly, the electrolyte's susceptibility to water decomposition leads to low stability over time, causing capacity decay. To address these issues, researchers have opted to limit areal loading and increase the electrolyte volume within the battery while maintaining a high C-rate. These limitations do not meet commercial requirements. To date, minimizing one problem has resulted in the addition of at least one (and often more) other problems. Therefore, unlike alkaline batteries, rechargeable Zn-MnO2 batteries have not yet been used in practical applications, and their development remains uncertain.

[0005] It has now been found, quite surprisingly, that the use of urea as an electrolyte additive in aqueous solutions of zinc salts provides unexpected improvements in cycling stability, particularly at high and / or low temperatures, without producing substantial negative effects on specific capacity, C-rate, electrolyte volume, and / or protection of the electrode surface by preventing dendrite growth.

[0006] Urea has been used as an additive in aqueous electrolytes for lithium-ion batteries because it has the ability to reduce the dissolution of lithium manganese oxide. 7 In electrochemical reactions driven by the dissolution / precipitation of MnO2, there was initially no indication that improvements in stability could be achieved. Summary of the Invention

[0007] According to one embodiment, the present invention relates to an aqueous electrolyte that can be advantageously used in Zn-MnO2 electrochemical devices, such as battery cells or batteries (battery packs). The electrolyte composition comprises water, a zinc salt (preferably ZnSO4), and urea.

[0008] The composition is preferably in a liquid or semi-liquid state (i.e., a viscous state). The zinc salt is advantageously partially or completely dissolved. The concentration of urea can reach or approach the saturation point of urea in the composition, for example, up to 10 mol (M). It will be readily understood that the operating temperature of the electrolyte must be considered when selecting the concentration of urea or any other component in the electrolyte composition. Unless otherwise stated, the operating temperature range of the electrolyte is -25°C to 70°C. According to a preferred embodiment, the operating temperature range is -13°C to 60°C, more preferably 5°C to 55°C, or even simply room temperature. Advantageously, the concentration of urea in the electrolyte of the present invention is selected in the range of 0.1 M to 10 M, preferably 2 M to 9 M, even more preferably 4 M to 8.5 M, particularly 8 M ± 0.5 M. The concentration of zinc salt, particularly zinc sulfate (ZnSO4), in the electrolyte composition is advantageously selected below the saturation point, particularly up to or below 3.5 M (the saturation concentration in water). A concentration of 1 M to 3.5 M is preferred, more preferably a concentration in the range of 2 M to 3 M, for example, about 3 M or 2 M. A concentration of water exceeding 24 M is even more preferred, and advantageously in the range of 26 M to 50 M.

[0009] According to one embodiment of the invention, the electrolyte composition consists of or is substantially composed of water, urea, and a zinc salt (e.g., ZnSO4). According to this embodiment, the urea concentration can be high, ranging from 4 M to 10 M, for example, 10 M, and the concentration of the zinc salt (especially ZnSO4) can range from 1.5 to 3.5 M, for example, approximately 2 M or 3 M.

[0010] According to one embodiment of the present invention, the zinc salt is selected from the group consisting of ZnSO4, Zn(OOCCH3)2, Zn(Otf)2, and Zn(BF4)2. Preferably, the zinc salt is ZnSO4.

[0011] According to another embodiment, the electrolyte composition comprises a mixture of zinc salts. Advantageously, the mixture of zinc salts is selected from a mixture of ZnSO4 and Zn(Otf)2, a mixture of Zn(Otf)2 and Zn(OOCCH3)2, and a mixture of Zn(BF4)2 and Zn(OOCCH3)2. However, it is preferable to select a mixture concentration that does not exceed the saturation concentration of any zinc salt in water.

[0012] According to another preferred embodiment of the invention, the electrolyte composition comprises at least one additional component and / or a mixture thereof.

[0013] The additional component can be a sulfate ion donor compound, such as H2SO4 or Zn4(OH)6SO4.

[0014] According to one embodiment, the at least one additional component is a sulfate ion donor, an organic solvent, or a mixture thereof.

[0015] Advantageously, the sulfate ion donor is selected from the group consisting of H2SO4, MnSO4, guanidine sulfate and zinc hydroxysulfate (Zn4(OH)6SO4).

[0016] Advantageously, the concentration of sulfate ion donors should be selected based on the saturation limit of zinc salts.

[0017] Sulfuric acid (H2SO4) is particularly preferred because this electrolyte exhibits improved stability at high temperatures (e.g., 55°C).

[0018] According to one embodiment, the concentration of sulfuric acid is between 0.1 M and 3 M, preferably between 0.1 M and 2 M, and more preferably between 0.25 M and 0.5 M.

[0019] Advantageously, H in the electrolyte composition + The concentration of ions is at least three times lower than the concentration of OH- ions.

[0020] In fact, H is preferred. + The amount of ions (determined by the concentration of H₂SO₄ and the volume of the electrolyte) should be at least three times lower than the amount of OH⁻ ions released by the electrochemical reaction (MnO₂ + 2 H₂O + 2e⁻ → Mn²⁺ + 4OH⁻), with the number of electrons depending on the experimental capacity. This ratio helps prevent anodic corrosion.

[0021] According to another embodiment, the concentration of sulfuric acid can be as high as 1.5 M, but advantageously ranges from 0.1 M to 1 M, more preferably from 0.1 M to 0.5 M, and even more advantageously from 0.5 M to 0.7 M.

[0022] According to one embodiment of the invention, the electrolyte composition consists of or is substantially composed of water, urea, a zinc salt (e.g., ZnSO4), and sulfuric acid. According to this embodiment, the urea concentration can be high, ranging from 5 M to 9.5 M, for example, about 8 M; the ZnSO4 concentration can range from 1.5 M to 3.5 M, for example, about 2 M or 3 M; and the H2SO4 concentration can range from 0.1 M to 0.8 M, for example, about 0.5 M. The added H... + The amount of ions should advantageously be maintained below 30% of the expected initial discharge capacity. This concentration helps neutralize the electrolyte and minimize zinc corrosion. According to a variant of the electrolyte composition of the invention, increasing the concentration of sulfate ions in the electrolyte may be advantageous, for example by adding Zn₄(OH)₆SO₄ powder to an electrolyte containing H₂SO₄ until saturation, as this will reduce the H₂ concentration in the solution.+ The amount.

[0023] According to one embodiment, the at least one additional component is an organic solvent selected from the group consisting of dimethyl sulfoxide (DMSO), acetonitrile, dimethylformamide, methyl acetate, and diol derivatives.

[0024] Preferably, the organic solvent is DMSO or acetonitrile, more preferably DMSO.

[0025] Advantageously, the concentration of the organic solvent is between 0.1 M and 6 M, preferably between 0.1 M and 4.6 M, more preferably between 0.1 M and 3 M, and even more preferably 1 M.

[0026] Alternatively, the additional component may be an organic compound, particularly dimethyl sulfoxide (DMSO), guanidine sulfate, or mixtures thereof. The concentration of DMSO can be up to 8 M, and is advantageously selected to not exceed the saturation point of the electrolyte composition at the operating temperature. A preferred concentration range of DMSO is 0.1 M to 4.6 M for cycling at room temperature, and this concentration can be higher if a higher temperature is selected (e.g., 55°C).

[0027] The concentration of guanidine sulfate can be up to 3 M, and is advantageously selected so as not to exceed the saturation point of the electrolyte composition at the operating temperature. The preferred concentration range of guanidine sulfate is 0.1 M to 2 M for cycling at room temperature, and this concentration can be higher if a higher temperature is selected (e.g., 55°C).

[0028] According to one embodiment of the invention, the electrolyte composition comprises or substantially comprises water, urea, a zinc salt (e.g., ZnSO4), and DMSO and / or guanidine sulfate, ultimately combined with sulfuric acid. According to this embodiment, the urea concentration may be, for example, about 8 M; the ZnSO4 concentration may range from 1.5 M to 3.5 M, for example, about 2 M or 3 M; the DMSO or guanidine concentration may range from 0.5 M to 3.5 M, for example, 2 M; and the sulfuric acid concentration may range from 0.1 M to 0.5 M, for example, 4 M.

[0029] According to a preferred embodiment of the invention, an additional component that may be present in the electrolyte of the invention is a zinc salt, such as Zn(Otf)₂ or Zn(OAc)₂. The concentration of this additional zinc salt may be from 0.1 M to 2 M.

[0030] Alternatively, or additionally, the additional component may be a manganese salt, particularly manganese sulfate. The concentration of this salt added is preferably up to 0.5 M. However, Zn in the electrolyte is preferred. 2+ and SO4 2- The concentration should be adjusted to avoid exceeding the saturation concentration of ZnSO4 (3.5 M in water).

[0031] According to one embodiment, the concentration of water in the electrolyte composition is greater than or equal to 23 M, preferably between 23 M and 50 M, and more preferably between 25 M and 35 M.

[0032] As those skilled in the art will understand, when in a liquid or viscous state, the concentrations of the various components of the electrolyte composition of the present invention will be advantageously selected to avoid precipitation of any components it may contain, particularly salts such as sulfates.

[0033] According to a preferred embodiment of the invention, the electrolyte composition does not contain lithium ions, and preferably does not contain either lithium ions or chloride ions.

[0034] According to another preferred embodiment of the invention, the electrolyte composition does not include chloride ions, because these ions can have some detrimental effects on the performance of the composition.

[0035] According to a preferred embodiment of the invention, the electrolyte composition does not include any additives typically used to improve the performance of the cathode (i.e., the manganese dioxide-containing electrode) itself. Such additives are in particular polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or any other metal oxide.

[0036] The electrolyte composition is particularly suitable for use in electrochemical devices, such as Zn-MnO2 battery cells and / or batteries. Such devices are also an object of the invention. The battery consists of one or more electrochemical battery cells. In particular, the electrolyte is suitable for use in the manufacture of rechargeable batteries, accumulators, or secondary batteries of this type, which can be charged, discharged to a load, and recharged multiple times. The electrolyte composition according to the invention can be used in small volumes (e.g., no more than 16 µl per milligram), thus reducing the size of the battery according to the invention.

[0037] Another object of the present invention is to provide an electrochemical battery cell comprising a first electrode consisting of or substantially composed of zinc, a second electrode consisting of MnO2, an electrolyte as described herein, a separator for separating the negative electrode from the positive electrode and conducting ions, and a current collector.

[0038] Zinc-containing electrodes can advantageously be treated by providing a series of stripping and deposition steps. This can be performed on Zn-Zn cell batteries at high current densities of 20 to 10 mA / cm². Advantageously, at least nine cycles of stripping and deposition are applied. Preferably, the treatment begins with a stripping step and ends with a deposition step. The electrolyte used during this pretreatment comprises an aqueous solution of zinc sulfate in the concentration range of 1 M to 3 M, advantageously 2 M. More preferably, the electrolyte also comprises guanidine sulfate in the concentration range of 1 M to 3 M, advantageously 2 M. Furthermore, it may be advantageous to limit the deposition and stripping steps to a charge of about 2 mAh. Guanidine sulfate appears to form a thin organic layer that can act as an SEI (solid electrolyte interface) reaction, protecting the anode from corrosion problems, particularly dendrite growth. The cycle life of Zn-MnO2 cell batteries or batteries with such a Zn electrode pretreated can therefore be significantly extended, for example, by up to 50 or 80 cycles. Even better results are obtained if the final step is a deposition step. This pretreatment step is another objective of the invention, and it is separate and distinct from the electrolyte of the invention; that is, it can be used independently and in conjunction with other types of electrolytes besides the electrolyte of the invention. The second electrode of the Zn-MnO2 battery cell of the invention can be at least partially or substantially composed of powder. This powder preferably comprises a mixture of MnO2 particles and conductive additives (such as carbon black). The average particle size of this powder, as measured by FEG-SEM images, is preferably less than 5 µm, more preferably between 0.5 µm and 2 µm, for example, 1.33 µm. This powder is preferably not substantially compressed or in a film-like configuration. Therefore, PTFE or PVDF are preferably not used as a binder, or even any adhesive material is used. Further preferably, MnO2 and conductive additives are present in the electrode at a mass ratio of 45 to 65, preferably 50 / 50. The second electrode has a concentration of up to 5 mg / cm³. 2 Up to 15 mg / cm 2 The optimal value is approximately 10 mg / cm³. 2 Surface load capacity.

[0039] The membrane separates the negative and positive electrodes and conducts ions. The membrane is advantageously made of glass fiber, preferably glass microfiber. A Class D Whatman glass microfiber membrane is preferred, with a pore size of 2.7 μm. However, Class A (1.7 μm pore size) or Class C (1.2 μm pore size) Whatman membranes can also be used. The glass microfiber membrane can advantageously be combined with a second membrane, such as Celgard or Bellcore.

[0040] The current collector can be made of any suitable material. It is preferable to avoid using aluminum or copper.

[0041] Another object of the present invention is the use of the electrolyte and / or electrochemical cell of the present invention in the manufacture of electrochemical devices, particularly rechargeable batteries.

[0042] Another object of the present invention is to use urea as an additive for stabilizing electrolyte compositions in Zn-MnO2 electrochemical devices, said compositions comprising H2O and zinc salts, particularly ZnSO4. The electrolytes and / or electrochemical devices, their uses, and examples are the same as described in this specification.

[0043] Another object of the present invention is a method for stabilizing an electrolyte composition for a Zn-MnO2 electrochemical device, the method comprising the step of providing a composition comprising H2O and a zinc salt (particularly ZnSO4) and urea, particularly by adding or mixing urea into a mixture comprising the zinc salt and water. The electrolyte and / or electrochemical device, its use, and examples are the same as described in this specification.

[0044] It should be understood that the eight specific examples provided below are given as illustrations and are not limitations. Attached Figure Description

[0045] Figure 1 The galvanostatic current and pressure curves of MnO2-Ketjenblack / Zn battery cells at 25°C are shown. These cells were cyclically used in A) 2 M ZnSO4, B) 2 M ZnSO4 in a 4.6 M DMSO aqueous solution, and C) the electrolyte of the present invention described in Example 1: 2 M ZnSO4 + 8 M urea. All cells were started up after a 4-hour settling period (or open circuit voltage, OCV).

[0046] Figure 2 A- Figure 2 F and Figure 2 H shows the galvanostatic charge-discharge curves of the MnO2-Ketjenblack / Zn battery cell described in Comparative Example 5 as a function of capacity, particularly: - Figure 2 The electrolyte used in battery A is a 2 M aqueous solution of ZnSO4; - Figure 2 The electrolyte used in battery B is a solution of 2 M ZnSO4 in DMF (4.6 M) and water; - Figure 2 The electrolyte used in C's battery is a solution of 2 M ZnSO4 in ethylene glycol (5.6 M) and water; - Figure 2 The electrolyte used in the D battery is a solution of 2 M ZnSO4 in DMSO (4.6 M) and water; - Figure 2 The electrolyte used in E's battery is a solution of 2 M ZnSO4 in glycerol (4.35 M) and water; - Figure 2 The electrolyte used in F's battery is a solution of 2 M ZnSO4 in glucose (2 M) and water; - Figure 2 The electrolyte used in H's battery is a solution of 2 M ZnSO4 in guanidine sulfate (2 M) and water.

[0047] Figure 2 G shows a constant current charge-discharge curve of the battery cell of the present invention as described in Example 4, with varying capacity, wherein the electrolyte is a solution of 2 M ZnSO4 in urea (8 M or 10 M) and water.

[0048] Figure 3 A, Figure 3 C and Figure 3 D shows the constant current charge-discharge curve of the battery cell described in Comparative Example 5 at 55°C as a function of capacity, with the electrolyte being A) 2 M ZnSO4 in water, C) a mixture of 2 M ZnSO4 in DMSO / water (4.6 M DMSO), and D) a mixture of 2 M ZnSO4 + 2 M guanidine sulfate in water.

[0049] Figure 3 B shows a constant current charge-discharge curve of the battery cell of the present invention described in Example 4 at 55°C as a function of capacity, wherein the electrolyte according to the present invention is a mixture of 2 M ZnSO4 + 4 M urea in water.

[0050] Figure 4 A – Figure 4 D shows the constant current charge-discharge curves of the Zn-MnO2 battery cell according to the present invention as a function of capacity, for A) electrolyte with a urea concentration of 8 M in water cyclic at 25°C, and C) electrolytes with urea concentrations of 4 M, 8 M and 10 M in water cyclic at 55°C; and their respective cycle performance (B and D).

[0051] Figure 5 A – Figure 5D shows the constant current charge-discharge curves of the Zn-MnO2 battery cells according to the present invention at 55°C as a function of capacity, for A) 8 M urea / 4.6 M DMSO / 2 M ZnSO4 aqueous electrolyte and 10 M urea / 2 M ZnSO4 aqueous electrolyte, and C) 10 M urea / 2 M ZnSO4 and 8 M urea / 2 M guanidine sulfate / 2 M ZnSO4 aqueous electrolyte; and their respective cycle performance (B and D).

[0052] Figure 6 Figure 6B shows the constant current charge-discharge curves of the Zn-MnO2 battery cell according to the present invention at 55°C as a function of capacity, as described in Examples 1 and 2a, for A) 2 M ZnSO4 + 10 M urea and 2 M ZnSO4 + 10 M urea + 0.5 M H2SO4 electrolyte, and for B) 3 M ZnSO4 + 10 M urea and 3 M ZnSO4 + 10 M urea + 0.5 M H2SO4 aqueous electrolyte.

[0053] Figure 7 A – Figure 7 D shows the galvanostatic charge-discharge curves of the electrochemical cell of the present invention described in Example 4 at 25°C, which has an electrolyte mixture of 2 M ZnSO4 + 8 M urea in water. A) At different charging cutoff voltages (0.65 V – 1.8 V and 0.65 V – 1.75 V) at a C / 4 rate (96 A / g). MnO2 C) under cycle, and C) at different discharge rates (96 A / g) MnO2 48 A / g MnO2 and 24 A / g MnO2 (B) and (D) loops; and their respective loop properties.

[0054] Figure 8 A shows the capacity variation of a urea-free electrochemical cell at 25°C with the number of cycles, having an electrolyte mixture of 2 M ZnSO4 + 4.6 M DMSO in water, cycled at different cutoff voltages (0.85 V – 1.75 V, 0.55 V – 1.8 V, 0.85 V – 1.8 V, and 0.65 V – 1.8 V), and its capacity at 96 A / g. MnO2 ratio and 480A / g MnO2 The loop performance is as follows.

[0055] Figure 8B shows the capacity variation of a urea-free electrochemical cell at 25°C with a cycle count, having an electrolyte mixture of 2 M ZnSO4 in water, with cutoff voltages of 0.85 V – 1.75 V, 0.55 V – 1.8 V, and 0.85 V – 1.8 V at C / 4 rate (96 A / g). MnO2 The cycle under the current, and its operation at C / 4 (96 A / g) MnO2 C / 8 (48 A / g) MnO2 ) and 1C (384 A / g MnO2 Cyclic performance at discharge rate.

[0056] Figure 9 The galvanostatic current curve of the electrochemical cell of the present invention described in Example 4, at 25°C over time, is shown after cycling in water in 2 M ZnSO4 + 10 M urea, with a resting period of 24 hours or 7 days, and the corresponding cycling performance. The 24-hour / 7-day OCV time is fixed at the end of charging and discharging.

[0057] Figure 10 A – Figure 10 D shows the constant current charge-discharge curve of the electrochemical cell of the present invention described in Example 4, which is cyclic in water in 3 M ZnSO4 + 10 M urea, and the corresponding cycling performance, with a current of ±0.624 mA (96 mA / g) at 5°C (AB). MnO2 The current at -13°C is ±0.312 mA (48 mA / g). MnO2 ).

[0058] Figure 11 A- Figure 11 E: Shows a constant current charge-discharge curve of the battery cell described in Example 6 as a function of capacity, which has an electrolyte mixture according to an embodiment of the present invention: 2M ZnSO4 + 10M urea + 1M DMSO or 1M guanidine sulfate or 1M MnSO4 or saturated Zn4(OH)6SO4, or 1M acetonitrile.

[0059] Figure 12 A- Figure 12 D: Shows a constant current charge-discharge curve of the battery cell described in Example 6 as a function of capacity, which has an electrolyte mixture according to an embodiment of the present invention: 2M Zn(OOCCH3)2 + 10M urea + 1M DMSO or 1M guanidine sulfate or 1M MnSO4 or saturated Zn4(OH)6SO4.

[0060] Figure 13 A- Figure 13 B: This shows a constant current charge-discharge curve of the battery cell of the present invention as described in Example 6, which has an electrolyte mixture according to an embodiment of the present invention: 2M Zn(BF4)2 + 10M urea + 0.1M DMSO or 1M guanidine sulfate or 1M MnSO4 or saturated Zn4(OH)6SO4.

[0061] Figure 14 A- Figure 14 C: Shows a constant current charge-discharge curve of the battery cell described in Example 6 as a function of capacity, which has an electrolyte mixture according to an embodiment of the present invention: 2M zinc tetrafluoroborate + 10M urea + 0.1M DMSO or 1M guanidine sulfate or 1M MnSO4 or saturated Zn4(OH)6SO4.

[0062] Example 1: Preparation of the electrolyte (ZnSO4 and urea in water) and electrochemical device according to the present invention.

[0063] Electrolyte synthesis Mix urea with Milli-Q ultrapure water and stir for 5 minutes. Then add ZnSO4 and stir the mixture until completely dissolved. The following final concentrations in water were used: 2 M ZnSO4 + 4 M urea; 2 M ZnSO4 + 8 M urea; 2 M ZnSO4 + 10 M urea; and 3 M ZnSO4 + 10 M urea.

[0064] battery cell MnO2 was synthesized by slowly adding 50 mL of 0.6 M Na2S2O8 dropwise to a round-bottom flask containing 125 mL of 0.2 M MnSO4. The reaction mixture was heated and magnetically stirred. The resulting precipitate was thoroughly washed with Milli-Q water, filtered through a cellulose ester filter, and then dried under vacuum (using a Büchi vacuum pump) at 100°C for 20 hours. The resulting MnO2 exhibited a needle-like aggregate morphology, with particles arranged radially, resembling a sea urchin structure, and a diameter of less than 1 µm. The particle size was advantageously maintained within the micrometer range to preserve a high specific capacity.

[0065] The MnO2 (positive) electrode is made of 50 wt% carbon black (Ketjenblack 600 JD – CAS No. 1333-86-4) and 50 wt.% MnO2, which are mixed together by hand grinding. The total mass of the cathode is fixed at 12.5 mg, which is equivalent to 5 mg / cm³. 2 Up to 10 mg / cm 2The areal load was determined. The cathode mixture was assembled by filling a glass fiber diaphragm (GF / D, 1.27 cm Ø).

[0066] The zinc anode (a 1 cm Ø Zn disc) was washed with ethanol only before being introduced into the battery cell.

[0067] In one example, the zinc anode underwent pre-cycling: two zinc metal electrodes, each 1.1 cm in diameter, were placed opposite each other in a 5 ml volume electrochemical cell filled with a 2 M ZnSO4 aqueous solution. The treatment involved a series of Zn deposition and Zn stripping cycles, repeated 9 times. The applied current density was 10 mA / cm². 2 The deposition / stripping process is limited to a charge of 2 mAh. Results obtained using electrodes treated with this process are shown in... Figure 5 C and Figure 5 In D, the pretreated Zn electrode is used with the electrolyte of the present invention, which is an aqueous mixture of 2 M ZnSO4 (2 M) and urea (10 M). In all other examples of the present invention, the zinc electrode is washed with ethanol only before use.

[0068] No pressure is applied when assembling the battery cells.

[0069] Tests were conducted at 25°C using stainless steel or titanium plungers, and at 55°C using glass carbon plungers.

[0070] Subsequently, 100 µL of the selected electrolyte was carefully added to the top of the diaphragm using a micropipette.

[0071] For all electrochemical tests, a two-electrode configuration was used with a PFA hardware Swagelok cell. The cell was started after 4 hours of OCV (unless an electrolyte containing H₂SO₄ was used), with a current density of ± 96 A / gMnO₂ and 100 µL of electrolyte. The cathode mass was kept constant at 12.5 mg for all experiments. The established cycle rates correspond to the C-rate of C / 4 (unless otherwise specified).

[0072] In addition, unless otherwise specified, the voltage window is set between 0.85 and 1.75 V. Figure 1 or between 0.65V and 1.8V ( Figure 2 and Figure 3 The C-multiplier used is C / 4.

[0073] Example 2: Preparation of the electrolyte (ZnSO4, urea and DMSO in water) and electrochemical device according to the present invention.

[0074] The electrolyte composition of 2 M ZnSO4 / 4.6 M DMSO was prepared in two steps. First, water and DMSO were mixed, and the resulting solution was used to dissolve 2 M ZnSO4 in a volumetric flask. Cells were prepared and tested as described in Example 1.

[0075] Example 3: Preparation of the electrolyte (ZnSO4 in water, urea and guanidine sulfate) and electrochemical device according to the present invention.

[0076] An 8 M urea / 2 M guanidine sulfate electrolyte composition was prepared according to the following steps: First, 2 M ZnSO4 was prepared, and the resulting solution was used to dissolve 10 M urea + guanidine sulfate in a volumetric flask. The battery cells were prepared and tested as described in Example 1.

[0077] Example 4: Preparation of the electrolyte (ZnSO4, urea and H2SO4 in water) and electrochemical device according to the present invention.

[0078] An electrolyte composition of 10 M urea / 3 M ZnSO4 / 0.5 M H2SO4 was prepared in two steps. First, 0.5 M H2SO4 was mixed with an aqueous solution of 2 M ZnSO4, and the resulting solution was used to dissolve 10 M urea in a volumetric flask.

[0079] When using this electrolyte for cycling at 55°C, the process should be started without an OCV (open circuit voltage) time to avoid damaging the anode.

[0080] The concentration of H₂SO₄ in the electrolyte can vary depending on experimental conditions. However, H + The amount of ions should always be kept below 30% of the expected experimental capacity to properly neutralize the electrolyte.

[0081] The battery cells were prepared and tested as described in Example 1.

[0082] Comparative Example 5: Preparation of an electrolyte (with or without other additives and solvents) and an electrochemical device consisting of ZnSO4 dissolved in water.

[0083] Various aqueous electrolytes were prepared in order to compare their performance with the electrolyte compositions according to the present invention.

[0084] 2 M ZnSO4 + 4.6 M DMSO, 2 M ZnSO4 + 5.6 M ethylene glycol, and 2 M ZnSO4 + 4.6 M DMF were prepared by mixing 2 volumes of Milli-Q ultrapure water with 1 volume of the corresponding organic solvents. The mixtures were stirred for 5 minutes, followed by the addition of ZnSO4 salts.

[0085] A similar procedure is used for the following electrolytes: 2 M ZnSO4 + 4.35 M glycerol, 2 M ZnSO4 + 2 M glucose, and 2 M ZnSO4 + 2 M guanidine sulfate.

[0086] Apart from the electrolyte used, the battery cells were prepared and tested as described in Example 1.

[0087] Example 6: Preparation of electrolyte according to the present invention.

[0088] Electrolyte synthesis An electrolyte composition containing zinc salt, urea, and sulfate ion donor or organic solvent in water is prepared as follows: Step 1: Mix urea with Milli-Q ultrapure water in a volumetric flask by hand or using a vortex mixer until completely dissolved.

[0089] Step 2: In another volumetric flask, add the zinc salt to the urea solution (from Step 1) and stir vigorously until completely dissolved.

[0090] Step 3: Add the sulfate ion donor or organic solvent to the solution.

[0091] The order of steps 1 and 2 can be interchanged; however, it is preferable to perform step 3 last.

[0092] The electrolyte composition has been prepared according to steps 1, 2, and 3 above. The following final concentrations are proposed: -2 M ZnSO4 + 10 M urea + 1 M DMSO -2 M ZnSO4 + 10 M urea + 1 M acetonitrile -2 M ZnSO4 + 10 M urea + 1 M guanidine sulfate -2 M ZnSO4 + 10 M urea + 1 M MnSO4 -2 M ZnSO4 + 10 M urea + ZHS (饱和) -2 M Zn(OOCCH3)2 + 10 M urea + 1 M DMSO -2 M Zn(OOCCH3)2 + 10 M urea + 1 M guanidine sulfate -2 M Zn(OOCCH3)2 + 10 M urea + 1 M MnSO4 -2 M Zn(OOCCH3)2 + 10 M urea + ZHS (饱和) -2 M Zn(BF4)2 + 10 M urea + 1 M DMSO -2 M Zn(BF4)2 + 10 M urea + ZHS (饱和) -1 M Zn(Otf)2 + 10 M urea + 1 M DMSO -1 M Zn(Otf)2 + 10 M urea + 1 M MnSO4 -2 M Zn(Otf)2 + 10 M urea + 1 M acetonitrile Different electrolyte compositions have been tested in Zn-MnO2 battery cells. The galvanostatic charge-discharge curves of these batteries as a function of capacity and their corresponding cycle performance are shown in [figure / description]. Figures 11 to 14 middle.

[0093] battery cell The corresponding battery cells were prepared according to Example 1, except that the anode was not pre-cycled.

[0094] In addition, unless otherwise specified, the voltage window is set between 0.65 and 1.8 V, and the C-multiplier used is C / 4.

[0095] Comment In the standard Zn-MnO2 cell, the intracellular pressure showed a significant decrease during the first 6 cycles (from ORR). In contrast, the pressure of the urea-containing electrolyte cell and the DMSO-containing electrolyte cell according to Example 1 remained stable during cycling at voltages from 0.65 to 1.75 V, and over a wider voltage range of 0.3 V to 1.8 V (see Example 1). Figure 1 ).

[0096] Figure 2 A and Figure 2 G shows the urea-containing electrolyte relative to the standard 2 M ZnMnO2 cell ( Figure 2 A) Improvements in capacity retention. Regarding organic solvents, only DMSO exhibited higher capacity retention during cycling compared to 2 M ZnSO4 electrolyte. This stability can be explained by the fact that the decomposition of solvated H2O is significantly reduced due to the formation of strong H2O-DMSO interactions. Regarding organic additives (or salts), glycerol and glucose showed low capacity retention. Figure 2 E and Figure 2 F). Urea (and guanidine) appear to significantly increase the cyclic stability of such systems. Figure 2 H and Figure 2G). The performance of 4M urea and 2M guanidine sulfate is comparable at 25°C, but not at 55°C. Figure 3 B and Figure 3 (D) At 55°C, urea exhibits better stability than both urea and DMSO. In fact, cycling at higher temperatures shows additional capacity during charging, likely due to side reactions (primarily water decomposition) that are exacerbated at such temperatures. These reactions pose critical problems during cycling, particularly because oxygen release can poison the zinc anode. Compared to urea, guanidine sulfate appears to decompose at 1.7 V, and DMSO also shows poorer performance (see [link to article]). Figure 3 ).

[0097] Despite the application of different currents, the urea-containing electrolyte according to the present invention maintains its excellent stability (see...). Figure 7 A to Figure 7 D), taking into account the behavior of DMSO electrolytes with or without additives under similar conditions (see D). Figure 8 This is a huge improvement. (For example...) Figure 7 As shown in B, the battery cell according to the present invention exhibits an efficiency of 99% and a high capacity retention of over 50 cycles, with a specific capacity of approximately 400 mAh / g (MnO2) and an areal capacity of 2-4 mAh / cm². 2 between.

[0098] When self-discharge conditions are applied by alternating cycles with a 24-hour OCV time, the performance of the individual cells is maintained after the discharge / charge rest period (see [link]). Figure 9 ).

[0099] The urea-containing electrolyte according to the present invention is much less affected by high temperatures (see Figure 4 B). In addition, increasing the urea concentration ( Figure 4 ) or add DMSO ( Figure 5 A and 5B) or guanidine or pretreated zinc electrode ( Figure 5 C and 5D) allow for further increases in the stability of the electrolyte of the present invention at high temperatures.

[0100] Surprisingly good performance was obtained by adding sulfuric acid to the electrolyte of this invention. For example... Figure 6 As shown, when the electrolyte of Example 4 was used, a significant capacity retention was obtained at 55°C.

[0101] The urea-containing electrolyte according to the invention also exhibits excellent stability at low temperatures. However, conductivity appears to be affected because we need to reduce the C-rate to C / 8 (48 A / gMnO2) to recover 80% of the capacity at 25°C.

[0102] Figure 11A mixture of 2 M ZnSO4 + 10 M urea + (DMSO or guanidine sulfate or MnSO4 or ZHS) and Figure 12 A mixture of 2 M Zn(OOCCH3)2 + 10 M urea + (DMSO or guanidine sulfate or MnSO4 or ZHS) showed good cycling performance, recovering over 2 mAh for 12.5 mg MnO2. This has the advantage of reducing the amount of water in the system, which may potentially reduce side reactions at high temperatures. However, we can emphasize the beneficial effect of SO4 ions on the system, as the best reported performance was achieved using ZnSO4 as the zinc salt in the electrolyte. Figure 12 Similar conclusions can be observed in [the study]. This is similar to the effect of an electrolyte mixture containing 2 M Zn(OOCCH3)2 + 10 M urea + 1 M DMSO. Figure 12 Compared to A, the addition of SO4 ions ( Figure 12 B- Figure 12 D) shows better performance.

[0103] Figure 13 It was shown that good stability could also be obtained using a mixture of 2 M Zn(BF4)2 + 10 M urea + (DMSO or ZHS).

[0104] Figure 14 The mixture of 2 M Zn(Otf)2 + 10 M urea + (DMSO or MnSO4 or acetonitrile) presented in the sample showed similarity to... Figure 11 Similar performance. However, we can note that the optimal capacity was obtained for the electrolyte mixture of 2 M Zn(Otf)2 + 10 M urea + MnSO4, which again highlights the beneficial role of SO4 ions in the conversion of MnO2.

[0105] List of references: 1.Yamamoto, T.&Shoji, T. Rechargeable ZnlZnSO, IMnO+peCells. Inorganica Chim Acta ,117, 27–28 (1986). 2.Shoji, T.&Yamamoto, T. Charging and discharging behavior of zinc-manganese dioxide galvanic cells using zinc sulfate as electrolyte. Journal of Electroanalytical Chemistry ,362, 153–157 (1993). 3.Shoji, T., Hishinuma, M.&Yamamoto, T. Zinc-manganese dioxidegalvanic cell using zinc sulphate as electrolyte. Rechargeability of thecell. J Appl Electrochem ,18, 521–526 (1988). 4.Xu, C., Li, B., Du, H.&Kang, F. Energetic Zinc Ion Chemistry: TheRechargeable Zinc Ion Battery. Angewandte Chemie ,124, 957–959 (2012). 5.Godeffroy, L. et al. Decoupling the Dynamics of Zinc HydroxideSulfate Precipitation / Dissolution in Aqueous Zn–MnO2 Batteries by OperandoOptical Microscopy: A Missing Piece of the Mechanistic Puzzle. Adv Energy Mater ,12, (2022). 6.Aguilar, I. et al. Identifying interfacial mechanisms limitationswithin aqueous Zn-MnO2 batteries and means to cure them with additives. Energy Storage Master ,53, 238–253 (2022). 7.Fitz, O. et al. Electrolyte Study with in Operando pH TrackingProviding Insight into the Reaction Mechanism of Aqueous Acidic Zn / / MnO2Batteries. ChemElectroChem ,8, 3553–3566 (2021). 8.Bischoff, C. F. et al. Revealing the Local pH Value Changes ofAcidic Aqueous Zinc Ion Batteries with a Manganese Dioxide Electrode duringCycling. J Electrochem Soc ,167, 020545 (2020).

Claims

1. An electrolyte composition for a zinc-manganese dioxide electrochemical device, said electrolyte comprising water, a zinc salt, and urea.

2. The electrolyte composition according to claim 1, wherein it comprises at least one additional component, said component being a sulfate ion donor or an organic solvent.

3. The electrolyte composition according to claim 2, wherein the sulfate ion donor component is selected from the group consisting of H2SO4, MnSO4, guanidine sulfate and zinc hydroxysulfate (Zn4(OH)6SO4).

4. The electrolyte composition according to any one of claims 1 to 3, wherein the concentration of urea is in the range of 0.1 M to 10 M.

5. The electrolyte composition according to any one of claims 1 to 4, wherein the concentration of the zinc salt ranges from 0.1 M to 3.5 M, preferably 3 M.

6. The electrolyte composition according to any one of claims 2 to 5, wherein the organic solvent is selected from the group consisting of dimethyl sulfoxide (DMSO), acetonitrile, dimethylformamide, methyl acetate and diol derivatives.

7. The electrolyte composition according to any one of claims 1 to 6, wherein the zinc salt is selected from the group consisting of ZnSO4, Zn(OOCCH3)2, Zn(Otf)2 and Zn(BF4)2, especially ZnSO4.

8. The electrolyte composition according to any one of claims 1 to 7, wherein the composition does not contain lithium ions, and preferably does not contain either lithium ions or chloride ions.

9. An electrochemical cell comprising a first electrode containing zinc, a second electrode containing MnO2, an electrolyte, a separator for separating a negative electrode from a positive electrode and conducting ions, and a current collector, wherein the electrolyte is the electrolyte as described in any of the preceding claims.

10. The electrochemical cell of claim 9, wherein the zinc-containing electrode is processed by a series of stripping and deposition steps, the processing being carried out by applying a current density in the range of 20 to 10 mA / cm² to the electrochemical cell comprising the electrode and another zinc-containing electrode and an electrolyte comprising an aqueous solution of zinc sulfate and / or an aqueous solution of guanidine sulfate.

11. The electrochemical cell according to claim 9 or 10, wherein the second electrode comprises or is substantially composed of powder, the powder preferably comprising a mixture of MnO2 particles and conductive additives such as carbon black.

12. The electrochemical cell according to any one of claims 9 to 11, wherein MnO2 and the conductive additive are present in a mass ratio of 45 to 65, preferably in a mass ratio of 50 / 50.

13. The electrochemical cell according to any one of claims 9 to 12, wherein the areal loading of the second electrode is 10 mg / cm². 2 .

14. Use of the electrolyte and / or electrochemical cell as described in any of the preceding claims for manufacturing an electrochemical device, such as a rechargeable battery.

15. Use of urea as an additive for stabilizing electrolyte compositions in Zn-MnO2 batteries, said compositions comprising H2O and zinc salts.

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