Pressurized carbon dioxide for use in stabilizing aqueous batteries

Abstract

A method of stabilizing an aqueous battery comprising a Zn anode and a MnO2 cathode is disclosed. The method can comprise exposing the Zn anode and the MnO2 cathode to pressurized CO2, whereby the aqueous battery is stabilized. An aqueous battery comprising a Zn anode and a MnO2 cathode, wherein the Zn anode and the MnO2 cathode have been exposed to pressurized CO2 is also disclosed.

Description

[0001] Attorney Docket No. 1306 / 196 PCT

[0002] PRESSURIZED CARBON DIOXIDE IN AQUEOUS BATTERIES AND APPROACHES

[0003] FOR GENERATING AND MAINTAINING CARBON DIOXIDE PRESSURE IN BATTERIES WITHOUT EXTERNAL GAS SUPPLY

[0004] CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0005] This application claims priority to and benefit of U.S. Provisional Patent Application Serial No. 63 / 701,713, filed October 1, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0006] TECHNICAL FIELD

[0007] The presently disclosed subject matter relates in some examples to pressurized carbon dioxide (CO2) in batteries, including aqueous batteries. The presently disclosed subject matter relates in some examples to approaches for generating and maintaining CO2 pressure in batteries without an external gas supply.

[0008] BACKGROUND

[0009] Aqueous Zn-MnO2 batteries are among the most attractive systems for stationary energy storage because both Zn and Mn02 are low cost but high-capacity electrode materials, and their combination with aqueous electrolytes can theoretically deliver safe batteries with close to 150 Watt-hour per kilogram (Wh / kg) energy density. This battery can operate in mild acidic or neutral aqueous electrolytes that are free of major safety and environmental concerns and hence hold great promises as more sustainable alternatives for lead acid batteries and Li- ion batteries for large scale stationary applications. Once installed, however, batteries for such stationary energy storage applications are subject to temperature variations across days and seasons and hence need robust performance for all-weather conditions. Unfortunately, both anode and cathode interfaces in aqueous Zn-Mn02 batteries suffer from instability and result in premature cycling failure even at ambient temperatures. Thus, approaches to enhance their performance represent an ongoing need in the art.

[0010] SUMMARY

[0011] This Summary lists several embodiments of the presently disclosed subject matter, and in many cases lists variations and permutations of these embodiments. This Summary is merely exemplary of the numerous and varied embodiments. Mention of one or more representative features of a given embodiment is likewise exemplary. Such an embodiment can typically exist Attorney Docket No. 1306 / 196 PCT with or without the feature(s) mentioned; likewise, those features can be applied to other embodiments of the presently disclosed subject matter, whether listed in this summary or not. To avoid excessive repetition, this Summary does not list or suggest all possible combinations of such features.

[0012] In accordance with some examples, the presently disclosed subject matter provides a method of stabilizing an aqueous battery comprising a Zn anode and a MnCh cathode is provided. In some examples, the method comprises exposing the Zn anode and the MnCh cathode to pressurized CO2, whereby the aqueous battery is stabilized.

[0013] In some examples, the the Zn anode comprises a ZnCO3-Zn(OH)2 layer.

[0014] In some examples, the MnCh cathode comprises ZnCCh.

[0015] In some examples, the pressurized CO2 is supplied from an external gas supply.

[0016] In some examples, the pressurized CO2 is provided from a molecule from which CO2 is derived.

[0017] In some examples, the molecule from which CO2 is derived comprises a carbonate.

[0018] In some examples, the molecule from which CO2 is derived is added to the aqueous battery.

[0019] In accordance with some examples, the presently disclosed subject matter provides an aqueous battery comprising a Zn anode and a MnCh cathode. In some examples, the Zn anode and the MnCh cathode have been exposed to pressurized CO2.

[0020] In some examples, the Zn anode comprises a ZnCO3-Zn(OH)2 layer.

[0021] In some examples, the MnCh cathode comprises ZnCCh.

[0022] In some examples, the pressurized CO2 is supplied from an external gas supply.

[0023] In some examples, the the pressurized CO2 is provided from a molecule from which CO2 is derived.

[0024] In some examples, the molecule from which CO2 is derived comprises a carbonate.

[0025] In some examples, the molecule from which CO2 is derived is added to the aqueous battery.

[0026] Accordingly, it is an object of the presently disclosed subject matter to provide a method for stabilizing an aqueous battery, and to provide an aqueous stabilized battery.

[0027] An object of the presently disclosed subject matter having been stated hereinabove, and which is achieved in whole or in part by the presently disclosed subject matter, other objects will become evident as the description proceeds hereinbelow. Attorney Docket No. 1306 / 196 PCT

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a plot of CO2-electrolyte interactions via13C NMR.

[0030] Figure 2 is a bar graph showing a comparison of ionic conductivities of the 2.0M Zn(C104)2 aqueous electrolyte with increasing CO2 pressure.

[0031] Figure 3 is a set of plots of cyclic voltammogram (CV) profiles for the deposition and stripping of zinc (Zn) on copper (Cu) current collector with (30 pounds per square inch (psi) CO2, dashed line) and without (0 psi, solid line) CO2) CO2 pressure (scan rate = 10 mV / s).

[0032] Figure 4 is a set of plots of CV profiles for the oxidative stability of Zn(C104)2 electrolyte with (dashed line) and without (solid line) CO2 pressure (scan rate = 10 mV / s).

[0033] Figure 5 is a plot showing a comparison of columbic efficiency for Zn plating and stripping on Cu current collector in electrolytes with (dashed line) and without (solid line) 30 psi CO2 at 50°C.

[0034] Figure 6 is a set of plots showing a comparison of Faradic efficiencies as a function of cycle numbers with and without CO2.

[0035] Figure 7 is a set of plots showing Raman spectroscopy of cycled Zn anode.

[0036] Figure 8 is a plot showing a x-ray diffraction pattern of cycled Zn anode.

[0037] Figure 9 is a set of Nyquist plots of Zn half cells acquired during cycling with and without pressurized CO2.

[0038] Figure 10 is a set of plots showing voltage profiles for Zn-MnCh batteries at 1C under different gas atmosphere.

[0039] Figure 11 is a set of plots showing cycling stability of Zn-MnCh batteries under presurized CO2 at 20°C and -30°C.

[0040] Figure 12 is a set of plots showing X-ray diffraction patterns of cycled MnCh electrode under different conditions as marked.

[0041] Figure 13 is a set of plots showing cycling stability of Zn-MnCh batteries assembled with different E / C ratio (electrolyte to capacity) under pressurized CO2.

[0042] Figure 14 is a set of plots showing cycling stability of Zn-MnCh batteries with the E / C ratio of 5 (electrolyte to capacity) under pressurized CO2 at different temperatures.

[0043] Figure 15 is a set of plots showing self-discharging behavior of Zn-MnCh batteries with (solid black line) and without (solid light gray line) pressured CO2.

[0044] Figure 16 is a set of plots showing self-discharging behavior of Zn anode with and without pressured CO2. Attorney Docket No. 1306 / 196 PCT

[0045] Figure 17 is a set of plots showing self-discharging behavior of MnCh cathode with and without pressured CO2.

[0046] Figure 18 is a plot of a13C NMR spectrum of the 1.0M Zn(C104)2 aqueous electrolyte with 10vol% PC additive after one day. The spectrum confirms generation of CO2 molecules in the electrolyte. The peak position and intensity were both stable for weeks.

[0047] Figure 19 is a set of plots showing a comparison of Zn anode Coulombic efficiency in aqueous electrolyte with different carbonate additives: base electrolyte = 1.0M Zn(C104)2 in water; initial Zn reservoir = 5 mAh; cycling condition: 1 mA; 0.5mAh per step, 50 cycles. The spectrum confirms generation of CO2 molecule in the electrolyte. The peak position and intensity were both stable for weeks.

[0048] Figure 20 is a set of plots showing a comparison of stability of Zn anode during repeated plating and stripping on Cu current collector in different electrolytes. The Coulombic efficiency on the Y-axes refers to the efficiency for each cycle. Cycling condition = 1 mA, and ImAh each step.

[0049] Figure 21 is a set of plots showing a cycling stability of Zn-Zn symmetric cell with and without PC additive. The addition of PC decreased the battery overpotential and extended the cycle life.

[0050] Figure 22 is a set of plots showing a comparison of cycling stabilities of Zn-MnCh prototype batteries with different carbonate additives. The addition of carbonate significantly improved cycling stability in all cases, with about 85% capacity retention after 500 cycles as compared with the only 5% retention in the carbonate free electrolyte.

[0051] Figure 23 is a set of plots showing a x-ray diffraction analysis of completely discharged MnCh cathode after cycling. The analysis confirms a CCh-mediated reaction mechanism that is the same as the case of external pressured CO2.

[0052] DETAILED DESCRIPTION

[0053] Aqueous Zn-Mn02 batteries are among the most attractive systems for stationary energy storage because both zinc (Zn) and manganese dioxide (Mn02) are low cost but high- capacity electrode materials, and their combination with aqueous electrolytes can theoretically deliver safe batteries with close to 150 Wh / kg energy density. These batteries can operate in mild acidic or neutral aqueous electrolytes that are free of major safety and environmental concerns. Thus, Zn-MnCh batteries hold great promise as a more sustainable alternative for lead acid batteries and Li-ion batteries for large scale stationary applications. Once installed, Attorney Docket No. 1306 / 196 PCT however, batteries for such stationary energy storage applications are subject to temperature variations across days and seasons and hence need robust performance for all-weather conditions. Unfortunately, both anode and cathode interfaces in aqueous Zn-MnCh batteries suffer from instability and result in premature cycling failure even at ambient temperatures. Although a plethora of advanced materials and electrolytes have been attempted in an effort to address key challenges associated with instability such as dendrite formation, low efficiency, decomposition of electrolyte, and dissolution of oxide cathodes, approaches to enable their robust performance under extreme hot and cold temperatures are mostly unknown.

[0054] As a typical metal anode, operation of a Zn anode in aqueous electrolyte suffers from side reactions such as hydrogen evaluation reaction and increase of local OH-. These side reactions compromise cycling efficiency and contribute to generation of loose Zn(OH)4 and ZnSChOH layer (and the associated decomposition product such as ZnO) that disrupt Zn-ion diffusion and foster growth of dendritic structures. Current strategies to address these challenges typically involve artificial solid electrolyte interface (SEI) layers, architectured anodes, and electrolyte modifications. Such SEI layers add a diffusion barrier for divalent Zn2+and durability of these layers for longer cycling are still questionable. In particular, SEI layers could readily detach from Zn surface during cycling, which would expose underneath fresh Zn surfaces and re-open their continuous side-reactions with electrolyte. Also, existing demonstrations are for room temperature or low temperatures, but the more problematic high temperature stability is unknown.

[0055] Similar to a Zn anode, cycling of MnCh in aqueous electrolytes also suffers from stability challenges and approaches to improve its stability are difficult to develop due to its complicated reaction pathway. The complication largely originates from the interplay between H+, Zn2+and possibly H2O insertion to MnCh, and the structural instability of electrochemically generated John-Teller active Mn3+cations that can disproportionate and release soluble Mn2+, resulting in cycling failure. Existing attempts at approaches are mostly centered around the use of pre-added Mn2+additives to suppress Mn2+dissolution. However, these approaches are fundamentally limited in terms of regulating the MnCh reaction pathway and therefore the improvement is limited. In addition, similar to the Zn anodes, existing results on MnCh cathodes were also mostly focused on ambient cycling, with some recent reports attempting to show that the MnCh at subfreezing temperature could shift the reaction pathway and enable more stable cycling. However, no effective approaches have been demonstrated to improve cycling stability at high temperatures. Attorney Docket No. 1306 / 196 PCT

[0056] Harnessing the interactions between gaseous species and battery components can open new opportunities in developing more stable batteries that would otherwise difficult or impossible to attain with conventional approaches. Stabilization of a Zn anode and a MnCh cathode by pressurized CO2 in the aqueous electrolyte is demonstrated herein in accordance with the presently disclosed subject matter. The high CO2 partial pressure contributes to the formation of an interface layer and can serve as a physical barrier to dendrite growth and Zn corrosion.

[0057] Aqueous Zn-MnCh batteries are promising for low cost and large-scale energy storage but face stability challenges at both anode and cathode interfaces, which can result in premature cycling failure and short calendar life. In some examples, the presently disclosed subject matter provides a method of stabilizing an aqueous battery comprising a Zn anode and a MnCh cathode. In some examples, the method comprises exposing the Zn anode and the MnCh cathode to pressurized CO2, whereby the aqueous battery is stabilized. In some examples, the Zn anode comprises a ZnCO3-Zn(OH)2 layer. In some examples, the MnCh cathode comprises ZnCCh. In some examples, the presently disclosed subject matter provides an approach to stabilize aqueous batteries using pressured CO2, with CO2 supplied from external sources. In some examples, the pressurized CO2 is supplied from an external gas supply.

[0058] In some examples, the presently disclosed subject matter pertains to the application of pressurized CO2 to stabilize both a Zn anode and a MnCh cathode for significantly improved cycling stability of Zn-MnCh batteries across all weather conditions from -30°C to 50°C. In some examples, the presently disclosed subject matter provides a Zn anode so stabilized. In some examples, the presently disclosed subject matter provides a MnCh cathode so stabilized. Representative, non-limiting functional mechanisms of pressured CO2 on both anode and cathode are described herein. For example, on the anode, a functional mechanism of pressured CO2 involves generating unique CO2 based ZnCO3-Zn(OH)2 solid electrolyte interphases that inhibit or even prevent dendrite growth and side reactions. This in situ formed surface layer not only suppresses Zn corrosion but also inhibits dendrite growth via guiding the Zn plating and stripping underneath the artificial layer. By way of additional example, pressurized CO2 can also stabilize a MnCh cathode by suppressing Mn2+dissolution and shifting the reaction mechanism that involves reversible formation of ZnCCh pathway. The presently disclosed subject matter further demonstrates example prototypes with experimentally verified unit energy density of 148 Wh / kg along with significantly improved shelving life, thereby providing Attorney Docket No. 1306 / 196 PCT examples of feasible solutions for all-weather aqueous batteries. In some examples, pressurized CO2 invokes stable aqueous interfaces for all-weather Zn-MnCh batteries.

[0059] In some examples, the pressurized CO2 is provided from a molecule from which CO2 is derived. In some examples, the molecule from which CO2 is derived comprises a carbonate. In some examples, the molecule from which CO2 is derived is added to the aqueous battery.

[0060] Thus, in some examples, the presently disclosed subject matter provides an approach that harnesses the power of CCh-cotaining sacrificial molecules, polymers and inorganic additives. Some examples of these additives include carbonate such as ethylene carbonate and propylene carbonate, polymers capable of reversible CO2 capture such as poly(urethane-urea)s, poly(carbonate-urethane)s, and inorganic carbonates such as zinc carbonate and manganese carbonate. Once added and sealed in batteries these additives slowly decompose to release CO2. These decomposition reactions are self-terminating once the CO2 pressure reaches a critical value, and as such, provide a mechanism to sustain CO2 pressure during long cycling. Batteries incorporating these additives exhibit significantly improved cycling stability.

[0061] In some examples, the presently disclosed subject matter provides a Zn anode. In some examples, the presently disclosed subject matter provides a Mn02 cathode. In some examples the presently disclosed subject matter provides an aqueous battery comprising a Zn anode and a MnCh cathode. In some examples, the Zn anode and the MnCh cathode have been exposed to pressurized CO2. In some examples, the Zn anode comprises a ZnCO3-Zn(OH)2 layer. In some examples, the MnCh cathode comprises ZnCCh. In some examples, the pressurized CO2 is supplied from an external gas supply. In some examples, the pressurized CO2 is provided from a molecule from which CO2 is derived. In some examples, the molecule from which CO2 is derived comprises a carbonate. In some examples, the molecule from which CO2 is derived is added to the aqueous battery.

[0062] Thus, in some embodiments, the presently disclosed subject matter provides novel battery designs, such as consumer grade battery designs that uses pressurized CO2 to extend cycling stability along with other benefits. In some embodiments, the presently disclosed subject matter provides methods of incorporating specific chemical species into the battery designs to induce and maintain a pressurized CO2 environment.

[0063] Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in this application, including the claims. Thus, for example, reference to "a component" includes a plurality of such components, and so forth. Attorney Docket No. 1306 / 196 PCT

[0064] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

[0065] As used herein, the term “about,” when referring to a value or to an amount of a composition, mass, weight, temperature, time, volume, concentration, percentage, etc., is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods or employ the disclosed compositions.

[0066] As used herein, ranges can be expressed as from “about” one particular value, and / or to “about” another particular value. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0067] As used herein, the term “and / or” when used in the context of a listing of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and / or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C and D.

[0068] In non-limiting Example 1 below, an approach was developed to stabilize aqueous batteries using pressured CO2, with CO2 supplied from external sources. Aqueous Zn-MnCh batteries are promising for low cost and large-scale energy storage but face stability challenges at both anode and cathode interfaces that results in premature cycling failure and short calendar life. The presently disclosed subject provides the application of pressurized CO2 to stabilize both Zn anode and MnCh cathode for significantly improved cycling stability of Zn-MnCh batteries across all weather conditions from -30°C to 50°C. Representative, non-limiting functional mechanisms of pressured CO2 on both anode and cathode are described herein. For example, on the anode, a functional mechanism of pressured CO2 involves generating unique CO2 based ZnCO3-Zn(OH)2 solid electrolyte interphases that retard or even prevent dendrite growth and side reactions. This in situ formed surface layer not only suppresses Zn corrosion Attorney Docket No. 1306 / 196 PCT but also inhibits dendrite growth via guiding the Zn plating and stripping underneath the artificial layer. By way of additional example, pressurized CO2 can also stabilize a MnCh cathode by suppressing Mn2+dissolution and shifting the reaction mechanism that involves reversible formation of ZnCCh pathway. The presently disclosed subject matter further demonstrates example prototypes with experimentally verified unit energy density of 148 Wh / kg along with significantly improved shelving life, thereby providing examples of feasible solutions for all-weather aqueous batteries. In some examples, pressurized CO2 invokes stable aqueous interfaces for all-weather Zn-MnCh batteries.

[0069] In non-limiting Example 2, an approach that harnesses the power of CCh-containing sacrificial molecules, polymers, and inorganic additives is described. Some examples of these additives include carbonate such as ethylene carbonate and propylene carbonate, polymers capable of reversible CO2 capture such as amides, and inorganic carbonates such as zinc carbonate and manganese carbonate. Once added and sealed in batteries these additives slowly decompose to release CO2. These decomposition reactions are self-terminating once the CO2 pressure reach a critical value, and as such, provide a mechanism to sustain CO2 pressure during long cycling. Batteries incorporating these additives exhibit significantly improved cycling stability.

[0070] EXAMPLES

[0071] The following Examples are included to further illustrate various embodiments of the presently disclosed subject matter. However, those of ordinary skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the presently disclosed subject matter.

[0072] EXAMPLE 1

[0073] Pressurized CO2 Invokes Stable Aqueous Interfaces for All-Weather Zn-MnCh Batteries

[0074] Physiochemical Properties of Electrolytes

[0075] It is well known that CO2 dissolves in and acidifies aqueous electrolytes via the chemical reaction of CO2 + H2O = H2CO3. The solubility of CO2 in water depends on gas pressure and increases slightly from 1.00 to 1.32 g / L with the CO2 partial pressure increase from 1 atm to 5 atm. The dissolution of CO2 in 2.0M Zn(C104)2 also increases its ionic Attorney Docket No. 1306 / 196 PCT conductivity slightly due to contributions from dissociated ions from dissolved CO2 (Figure 2) The nature of solvated CO2 as a function of pressure was examined by13C NMR (Figure 1), which confirms carbonyl group and increased portion of HCCh' and unassociated CO2 molecules with higher CO2 pressure.

[0076] Figure 3 and 4 compare the cyclic voltammogram (CV) profiles of 2.0 M Zn(C104)2 with and without pressurized CO2 acquired using a home-made gas cell. The electrolyte was purged with argon (Ar) to eliminate residual gas prior to cell assembly. The Zn plating in CO2 pressurized electrolytes exhibited similar overpotential and slightly reduced plating current, but the Faradic efficiency was consistently improved for all tests. Without wishing to be bound by any particular theory of operation, this can be attributed to the formation of surface layers that effectively suppress hydrogen evolution with the compromise of slightly increased Zn- ions diffusion resistance. The anodic stability was similar with a cut off voltage of 2.1 V as compared to Zn on stainless steel current collector.

[0077] The reversibility and kinetics of Zn2+ / Zn redox under CO2 pressures were quantified via galvanostatic testing of Zn / / Cu half cells at 50°C. The cell in CCh-free electrolyte exhibited a typical low efficiency of 66% at 50°C, which is expected due to more irreversible reactions at the Zn anode as temperature increases. The battery with 30 psi CO2 exhibited 96.6% efficiency as quantified in Figure 5, and the high efficiency drops if the CO2 pressure is released as shown in Figure 6, confirming the high efficiency is a result of CO2 pressure.

[0078] Analysis of cycled anode suggests evident presence of SEI layers on Cu foil. This layer appears hydrated and could quickly dehydrate and detach from electrode surface within few hours of exposing in air. Structural and spectroscopic characterizations of dried SEI layer identified ZnCO3Zn(OH)2 as the main component generated under pressurized CO2 (Figures 7-8). This layer was formed in situ during cycling and appears fully stabilized with the few cycles, as supported by the surface and thickness characterization via SEM. The stable film has approximately 500 nm in thickness. In addition, this film has uniform distribution throughout, as a series depth profile of XPS spectra acquired with stepwise Ar+sputtering show that ZnCCh always exist.

[0079] The presence of pressured CO2 played a role in the generation of the surface protection layer, such that the initial hydrogen evolution side reaction associated with Zn plating generated OH' at electrode surface. This pH change fosters a chemical precipitation reaction between Zn2+and COs2' that results in deposition of ZnCO3Zn(OH)2. Driving force for formation of such layer is the most pronounced at electrode surface where OH- was generated. As such, the Attorney Docket No. 1306 / 196 PCT interface appears Zn / / ZnCO3-Zn(OH)2 / / Zn2+. The function of such a layer toward Zn protection and avoidance of hydrogen evolution reaction is already known, but its uses for batteries has been unsuccessful due to instability during cycling. But, in the present study, its integrity can be well maintained by external CO2 pressure since this layer is self-healing as any broken SEI would induce side-reaction and formation of OH- at the broken site, thus forming new layers. This also means the thickness of this layer is self-limiting as the further growth is terminated as soon as no additional OH- can be generated, as can be supported by the nearly unchanging Faradic efficiency for over 1000 cycles.

[0080] The presence of surface layers slightly increased the interfacial charge-transfer resistance (Ret) slightly due to additional diffusion barriers for Zn2+moving throughout the layer, but also stabilized the electrode with nearly no change in Ret during cycling. Batteries cycled without CO2, on the other hand, despite of exhibiting smaller initial resistance, experienced much higher increases in Ret during 100 cycles (Figure 9). The results also confirm good Zn2+ion diffusion kinetics throughout the layer.

[0081] Similar formation of such surface structure and enhanced cycling stability was also observed from 20°C and -30°C. In particular, this interface enabled 6000 hours of stable cycling with efficiencies exceeding 99% at 2 mA cm'2. The batteries are still running without clear signs of failure. This suggests intrinsic stability because of both CO2 protection and reduced side-reactions at low temperatures. The summary of these results confirms outstanding performance for all-weather operations.

[0082] Electrochemistry of M11O2 cathode under pressurized CO2

[0083] Pressured CO2 also enabled stable cycling of MnCh under all-weather temperatures by functioning as a key reactant and shifting the cathode reaction pathway. This was confirmed with well-defined, fiber shaped a-MnCh cathode that were synthesized following our recent works (e.g., S. Gao, B. Li, H. Tan, F. Xia, O. Dahunsi, W. Xu, Y. Liu, R. Wang, Y. Cheng, High-Energy and Stable Subfreezing Aqueous Zn-MnO2 Batteries with Selective and Pseudocapacitive Zn-Ion Insertion in Mn02. Adv. Mater. 2022, 34, 2201510). Briefly, the electrodes were prepared as free-standing electrodes with typical mass loading of 3.5 mg cm'2. 10 wt% super-P carbon black was primary used as the conducting additive, but it was replaced with equivalent carbon nanofiber for ex situ electron microscope analysis of cycled electrodes to avoid interferences between spherical carbon black and the MnCh discharge products. Attorney Docket No. 1306 / 196 PCT

[0084] Although high effective on improving cycling stability, no Mn2+additives were added to the electrolyte to better access the true reaction mechanism.

[0085] MnCh cathodes exhibited CO2 pressure dependent electrochemical responses as shown in cells different CO2 pressure and external gases (O2 or Ar, all at 50°C, Figure 10). The differences are mostly associated with the upshift of both charge and discharge voltage profiles, as the specific capacities were similar. More importantly, the battery exhibited significantly improved stability in response to CO2 (Figure 10). The battery without CO2 exhibited rapid cycling decay and degraded almost completely within ~ 50 cycles. Batteries with 15 psi CO2, although still exhibited decay for the initial 10 cycles, maintained at ~ 120 mAh g'1for the reminder of the 500 cycles. The best result was observed with 30 psi CO2, with high initial retention and 50% retention for 500 cycles. The improved stability is further corroborated with the much smaller and nearly unchanging amount of leached Mn2+and the stable charge-transfer resistance (Ret), and the voltage profiles at the 500thcycle.

[0086] Although CO2 can be an active material for batteries as demonstrated in various metal- CO2 batteries, contribution of CO2 Faradic reactions to the observed capacity here was excluded based on the corroboration of three facts: 1) battery capacity has no direct correction with CO2 pressure as shown; 2) previous evidences with metal-CCh batteries identified that the discharge plateau for CO2 are generally ~ 0.5 V vs RHE (or 0.2V vs. Zn), and this is much lower than the voltage plateaus of interests here, and as such 3) capacity of the battery with 30 PSI discharged to 0.2V has similar capacity.

[0087] The dependence of voltage profiles on CCh-pressure suggests presence of a reaction mechanism that is associated with CO2. In the absence of CO2, discharge of MnCh in neutral electrolytes starts with H+insertion with the co-generation of OH', resulting in electrochemical formation of MnOOH chemical precipitation of Zn(C104)0H with electrolyte anions (Figure 12). This mechanism gradually shifts to Zn2+insertion at subfreezing reaction temperatures as demonstrated in our recent work but approaches to modulate mechanism at room temperature and beyond have not been identified. Without wishing to be bound by any particular theory of operation, the presence of CO2 appears as a new approach to modulate reaction mechanism particularly at ambient and elevated temperatures, as the formation of ZHS was replaced by the more favorable chemical formation of ZnCCh. The presence of ZnCCh was clearly confirmed with XRD analysis of discharged electrodes after 5 cycles. Similar as the anode passivation layer, well-crystalline ZnCCh was gradually emerged via an activation process during the initial few cycles, but amorphous ZnCCh was observed with the first cycle. Attorney Docket No. 1306 / 196 PCT

[0088] In references with ex situ XRD, electron microscope, elemental and X-ray photoelectron spectroscopic analysis of cycled MnCh cathode, we rationalized that the initial discharge starts with H+into MnOOH and with the contemporary formation of amorphous ZnCCh. The unstable MnOOH likely proceeds in a disproportion reaction and phase conversion to spinel ZnMnOx with battery cycling. High resolution electron microscope analysis on the basis of elemental and diffraction analysis reveals that electrochemically formed ZnCO3were spherical in shape and free from Mn2+ions, and wrap around initial fiber shaped Mn02. The phase conversion gradually fragmented and exfoliated into crumpled sheets, an observation similar with the cycling at freezing temperatures, and perhaps with generating soluble Mn2+intermediates. Formation of ZnCO3 was a result of electrochemical reaction of MnCh. As such, the reaction most likely proceeds as:

[0089] Activation step: 2OH’

[0090] Stabilized cycling:

[0091] 2 ZnMn3O7+ 2H2O + Zn2+— > 3 ZnM C + 4OH' (electrochemical reaction)

[0092] 4OH' + 2CO2 + 2 Zn2+— 2ZnCO3+ 2H2O (chemical reaction)

[0093] Kinetics of this mechanism is temperature dependent and can be promoted by operating at 50°C. Such a mechanism was also observed at room temperature, although the emergence of ZnCO3appears much slower. Figure 11 compares the cycling stability at room temperature and -30°C, where the specific capacity reached to 220 and 140 mAh / g at 20°C and -30°C, respectively, confirming the feasibility of all-weather performance, overcoming the barrier associated with battery stability during dramatic temperature changes as expected when deployed as stationary batteries.

[0094] All-weather full cells performance:

[0095] The much-improved reversibility of Zn anode and MnCh cathode with pressured CO2 suggest durable cycling under realistic conditions. This was confirmed by high energy density prototype cells with a negative-to-positive electrode capacity (N / P) ratio of - 1.5 using thick MnCh cathodes (~ 30 mg cm’2) and electroplated Zn anodes (~ 11.0 mAh cm’2). Battery assembled under such condition delivers a high unit-level energy density of 150 Wh / kg aqueous batteries. Figure 13 compares the cycling stability of batteries with different Attorney Docket No. 1306 / 196 PCT electrolyte-to-capacity (E / C) ratios, where high initial capacities exceeding 8.1 mAh were obtained with a E / C ratio of 5 and 7, corresponding to experimentally verified high energy densities of 148 and 119 Wh kg'1. The cycling stability of these batteries reveals nearly 70% retention for 100 cycles at 0.1C for the one with a E / C ratio of 7. This battery was dissembled after 100 cycles at the fully charged state and the remaining electroactivity on the cycled MnCh cathode and Zn anode was quantified by pairing with fresh cell components as 98% and 85% compared with the initial capacity, respectively, confirming their high reversibility. These experimentally verified unit-level energy densities are much higher compared with typical literature values and commercial Li-ion batteries and lead-acid batteries. Figure 14 is a set of plots showing cycling stability of Zn-MnCh batteries with the E / C ratio of 5 (electrolyte to capacity) under pressurized CO2 at different temperatures.

[0096] One major issue that is often overlooked is the shelfing life of batteries, especially for uses in stationary energy storage that involves cross-season energy storage. Charged electrode surfaces are inherently unstable, and gradually decay with spontaneous chemical reactions with electrolytes and within electrodes. The self-discharge behavior with and without CO2 are compared in Figure 15, which shows the capacity retention was 85.5% and 56.3% for batteries with and without 30PSI CO2. The self-discharge under pressured CO2 is mostly associated with cathode degradation as confirmed from capacity quantification after aging (Figure 16-17). Without wishing to be bound by any particular theory of operation, the new mechanism with the presence of CO2 significantly boosted the shelf life, making the battery more feasible for seasonable storage.

[0097] EXAMPLE 2

[0098] Approaches for Generating and Maintaining CO2 Pressure in Batteries without External Gas Supply

[0099] This Example is based on Example 1 above, which targets stable cycling of Zn-MnCh batteries for smart grids and transportation applications. This battery is promising because it is cheap, environmentally friendly, and does not need critical minerals. Manufacturing and supply chains of materials for this battery are relatively mature from commercialization of alkaline Zn-MnCh batteries (AA, AAA batteries). However, current Zn-MnCh batteries cannot be cycled and must be disposed once finished discharging. Technologies that can enable the stable cycling of these batteries, while at comparable cost, have significant potential to disrupt energy storage markets. Attorney Docket No. 1306 / 196 PCT

[0100] Example 1 identifies the use of pressurized CO2 as an approach to stabilize both cathode and anode interfaces in aqueous Zn-MnCh batteries, enabling durable cycling across a wide range of temperatures. However, the CO2 was provided from external sources, which employs additional components and infrastructural supports.

[0101] In Example 2, the use of sacrificial additives that can be added to the battery during manufacturing is described. These additives generate and maintain CO2 pressures throughout the service life of Zn-MnCh batteries. These additives may be added as components of the electrolyte, separator, cathode, anode, or any combination of the foregoing list.

[0102] These additives can be small molecules such as the various carbonates developed for Li-ion and Na-ion batteries, CO2 or carbonate-bearing polymers / inorganic particles, as developed for CO2 capture, and inorganic carbonates or hydroxide-carbonate such as zinc carbonate and manganese carbonate.

[0103] Some examples of carbonates include linear alkyl carbonates such as di ethyl carb onate and dimethylcarbonate and cyclic alkyl carbonate such as propylene carbonate and ethylene carbonate. Fluorinated carbonates (non-limiting examples mentioned below) are also good examples due to their better CO2 generating capability.

[0104] The presently disclosed subject matter, as exemplified by this representative Example 2, applies to substantially all Zn-MnCh configurations. In a typical configuration, the Zn anode can be Zn foil and Zn particles coated on current collectors, electrolytes can be Zn salts dissolved in aqueous or nonaqueous solvents, and cathodes can be various configurations incorporating various forms of MnCh particles.

[0105] Some example battery data are provided below. In these examples PC= propylene carbonate, TFPC=trifluropropylene carbonate; EC=ethylene carbonate; FEMC = methyl (2,2,2-trifluoroetyl) carbonate.

[0106] Referring to Figure 18, NMR spectra confirming the generation of CO2 once carbonate was added to the electrolyte are shown. Particularly, Figure 18 shows13C NMR spectrum of the 1.0M Zn(C104)2 aqueous electrolyte with 10 vol% PC additive after one day. The spectrum confirms generation of CO2 molecule in the electrolyte. The peak position and intensity were both stable for weeks. Thus, the NMR confirms stable presence of CO2 after weeks. The spectra were acquired using a special NMR sample tube that is capable of air-tight sealing and withstanding gas pressures.

[0107] Figures 19-21 provide systematic evaluation on the stability of Zn anode in aqueous electrolyte, with different types of carbonates added as additive. In all cases, the addition of Attorney Docket No. 1306 / 196 PCT carbonate significantly improves the plating and stripping efficiency of Zn, as well as the stability of these processes over repeated battery cycles.

[0108] Figure 19 shows a comparison of Zn anode coulombic efficiency in aqueous electrolyte with different carbonate additives: base electrolyte = 1.0M Zn(C104)2 in water; initial Zn reservoir = 5 mAh; cycling condition: 1 mA; 0.5mAh per step, 50 cycles.

[0109] Figure 20 shows a comparison of stability of Zn anode during repeated plating and stripping on Cu current collector in different electrolytes. The Coulombic efficiency on the Y- axes refers to the efficiency for each cycle. Cycling condition = 1 mA, and ImAh each step.

[0110] Figure 21 shows cycling stability of Zn-Zn symmetric cell with and without PC additive. The addition of PC decreased the battery overpotential and extended the cycle life.

[0111] Figure 22 shows comparison of cycling stabilities of Zn-MnCh prototype batteries with different carbonate additives. The addition of carbonate significantly improved cycling stability in all cases, with about 85% capacity retention after 500 cycles as compared with the only 5% retention in the carbonate free electrolyte.

[0112] Figure 23 shows X-ray diffraction analysis of completely discharged MnCh cathode after cycling. The analysis confirms a CCh-mediated reaction mechanism that is the same as the case of external pressured CO2.

[0113] All references listed in the instant disclosure, including but not limited to all patents, patent applications and publications thereof, scientific journal articles, and database entries are incorporated herein by reference in their entireties to the extent that they supplement, explain, provide a background for, and / or teach methodology, techniques, and / or compositions employed herein. The discussion of the references is intended merely to summarize the assertions made by their authors. No admission is made that any reference (or a portion of any reference) is relevant prior art. Applicants reserve the right to challenge the accuracy and pertinence of any cited reference.

[0114] It will be understood that various details of the presently disclosed subject matter may be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.

Claims

Attorney Docket No. 1306 / 196 PCTCLAIMSWhat is claimed is:

1. A method of stabilizing an aqueous battery comprising a Zn anode and a MnCh cathode, the method comprising exposing the Zn anode and the MnCh cathode to pressurized CO2, whereby the aqueous battery is stabilized.

2. The method of claim 1, wherein the Zn anode comprises a ZnCO3-Zn(OH)2 layer.

3. The method of claim 1 or claim 2, wherein the MnCh cathode comprises ZnCCh.

4. The method of any one of claims 1-3, wherein the pressurized CO2 is supplied from an external gas supply.

5. The method of any one of claims 1-3, wherein the pressurized CO2 is provided from a molecule from which CO2 is derived.

6. The method of claim 5, wherein the molecule from which CO2 is derived comprises a carbonate.

7. The method of claim 5 or claim 6, wherein the molecule from which CO2 is derived is added to the aqueous battery.

8. An aqueous battery comprising a Zn anode and a MnCh cathode, wherein the Zn anode and the MnCh cathode have been exposed to pressurized CO2.

9. The aqueous battery of claim 8, wherein the Zn anode comprises a ZnCCh- Zn(OH)2 layer.

10. The aqueous battery of claim 8 or claim 9, wherein the MnCh cathode comprisesZnCCh.Attorney Docket No. 1306 / 196 PCT11. The aqueous battery of any one of claims 8-10, wherein the pressurized CO2 is supplied from an external gas supply.

12. The aqueous battery of any one of claims 1-3, wherein the pressurized CO2 is provided from a molecule from which CO2 is derived.

13. The aqueous battery of claim 12, wherein the molecule from which CO2 is derived comprises a carbonate.

14. The aqueous battery of claim 12 or claim 13, wherein the molecule from which CO2 is derived is added to the aqueous battery.

Images